Rabbi Amichai Lau Lavi's Teshuvah on Intermarriage: A source primer
(ב) וּנְתָנָ֞ם יְהוָ֧ה אֱלֹהֶ֛יךָ לְפָנֶ֖יךָ וְהִכִּיתָ֑ם הַחֲרֵ֤ם תַּחֲרִים֙ אֹתָ֔ם לֹא־תִכְרֹ֥ת לָהֶ֛ם בְּרִ֖ית וְלֹ֥א תְחָנֵּֽם׃ (ג) וְלֹ֥א תִתְחַתֵּ֖ן בָּ֑ם בִּתְּךָ֙ לֹא־תִתֵּ֣ן לִבְנ֔וֹ וּבִתּ֖וֹ לֹא־תִקַּ֥ח לִבְנֶֽךָ׃ (ד) כִּֽי־יָסִ֤יר אֶת־בִּנְךָ֙ מֵֽאַחֲרַ֔י וְעָבְד֖וּ אֱלֹהִ֣ים אֲחֵרִ֑ים וְחָרָ֤ה אַף־יְהוָה֙ בָּכֶ֔ם וְהִשְׁמִידְךָ֖ מַהֵֽר׃

(2) and the LORD your God delivers them to you and you defeat them, you must doom them to destruction: grant them no terms and give them no quarter. (3) You shall not intermarry with them: do not give your daughters to their sons or take their daughters for your sons. (4) For they will turn your children away from Me to worship other gods, and the LORD’s anger will blaze forth against you and He will promptly wipe you out.

וגניבא משמיה דרב אמר כולן משום עבודת כוכבים גזרו בהן דכי אתא רב אחא בר אדא א"ר יצחק גזרו על פיתן משום שמנן מאי אולמיה דשמן מפת אלא על פיתן ושמנן משום יינן ועל יינן משום בנותיהן ועל בנותיהן משום דבר אחר ועל דבר אחר משום ד"א

The Gemara presents another opinion. And Geneiva says in the name of Rav: Gentiles’ bread, oil, wine, and daughters were all decreed upon due to the concern that Jews might participate in idol worship with gentiles as a result of intermingling with them. As, when Rav Aḥa bar Adda came from Eretz Yisrael to Babylonia he said that Rabbi Yitzḥak says: They decreed a prohibition upon their bread due to their oil. The Gemara asks: In what way is the prohibition with regard to oil stronger than the prohibition with regard to bread? That is, why does the primary concern relate to the oil of gentiles rather than their bread? The Gemara offers a different interpretation: Rather, they issued a decree prohibiting their bread and their oil due to their wine. And they issued the decree prohibiting their wine due to the fact that this leads to familiarity, and Jews will come to marry their daughters. And they issued a decree prohibiting their daughters due to something else, idolatry. And they further issued a decree on something else due to something else, which will be explained by the Gemara.

בנותיהן דאורייתא היא דכתיב (דברים ז, ג) לא תתחתן בם דאורייתא ז' אומות אבל שאר עובדי כוכבים לא ואתו אינהו וגזור אפילו דשאר עובדי כוכבים ולר"ש בן יוחי דאמר (דברים ז, ד) כי יסיר את בנך מאחרי לרבות כל המסירות מאי איכא למימר אלא דאורייתא אישות דרך חתנות ואתו אינהו גזור אפילו דרך זנות
It was stated that the prohibition against marrying the daughters of gentiles was decreed on account of idolatry. The Gemara raises an objection: But the prohibition against marrying their daughters is prescribed by Torah law, as it is written: “Neither shall you make marriages with them” (Deuteronomy 7:3). The Gemara explains: By Torah law intermarriage is prohibited only with the seven Canaanite nations, but intermarriage with the other nations of the world is not prohibited, and the students of Shammai and Hillel came and decreed that intermarriage is prohibited even with the other nations. The Gemara asks: And according to the opinion of Rabbi Shimon bar Yoḥai, who says that the subsequent verse: “For he will turn away your son from following Me” (Deuteronomy 7:4) serves to include all who turn away one’s son from God, i.e., all gentiles, what is there to say? Rather, by Torah law only sexual relations by way of marriage are prohibited, and they came and decreed that sexual relations are prohibited even by way of licentiousness.

(א) יִשְׂרָאֵל שֶׁבָּעַל עַכּוּ''ם מִשְּׁאָר הָאֻמּוֹת דֶּרֶךְ אִישׁוּת. אוֹ יִשְׂרְאֵלִית שֶׁנִּבְעֲלָה לְעַכּוּ''ם דֶּרֶךְ אִישׁוּת הֲרֵי אֵלּוּ לוֹקִין מִן הַתּוֹרָה שֶׁנֶּאֱמַר (דברים ז ג) "לֹא תִתְחַתֵּן בָּם בִּתְּךָ לֹא תִתֵּן לִבְנוֹ וּבִתּוֹ לֹא תִקַּח לִבְנֶךָ". אֶחָד שִׁבְעָה עֲמָמִין וְאֶחָד כָּל אֻמּוֹת בְּאִסּוּר זֶה. וְכֵן מְפֹרָשׁ עַל יְדֵי עֶזְרָא (נחמיה י לא) "וַאֲשֶׁר לֹא נִתֵּן בְּנֹתֵינוּ לְעַמֵּי הָאָרֶץ וְאֶת בְּנֹתֵיהֶם לֹא נִקַּח לְבָנֵינוּ":

(ב) וְלֹא אָסְרָה תּוֹרָה אֶלָּא דֶּרֶךְ חַתְנוּת אֲבָל הַבָּא עַל הַכּוּתִית דֶּרֶךְ זְנוּת מַכִּין אוֹתוֹ מַכַּת מַרְדּוּת מִדִּבְרֵי סוֹפְרִים. גְּזֵרָה שֶׁמָּא יָבוֹא לְהִתְחַתֵּן.

(1) If a Jewish person sleeps with a non-Jew in the way of married people, they receive biblically ordained lashes, as it says “You shall not intermarry with them: do not give your daughter to their sons or take their daughters for your sons.” (Deuteronomy 7:3) The same law is true concerning the seven nations of the land of Canaan and all other nations. This is also explained by Ezra, “We will not give our daughters in marriage to the peoples of the land, or take their daughters for our sons.” (Nehemiah 10:31)

2) And the Torah only prohibited marriage, but to come upon a Cuthite woman through harlotry you gve him lashes according to the words of the prophets. And this is a decree lest you come to marry them.

(ט) הָאוֹמֵר יְבָרְכוּךָ טוֹבִים, הֲרֵי זוֹ דֶּרֶךְ הַמִּינוּת. עַל קַן צִפּוֹר יַגִּיעוּ רַחֲמֶיךָ, וְעַל טוֹב יִזָּכֵר שְׁמֶךָ, מוֹדִים מוֹדִים, מְשַׁתְּקִין אוֹתוֹ. הַמְכַנֶּה בָעֲרָיוֹת, מְשַׁתְּקִין אוֹתוֹ. הָאוֹמֵר, וּמִזַּרְעֲךָ לֹא תִתֵּן לְהַעֲבִיר לַמֹּלֶךְ (ויקרא יח), וּמִזַרְעָךְ לֹא תִתֵּן לְאַעְבָּרָא בְּאַרְמָיוּתָא, מְשַׁתְּקִין אוֹתוֹ בִנְזִיפָה:

(9) A person who, in his prayers to the Almighty, says, "The good shall [alone] bless thee," acts in a heretical manner; if he says, "Even to birds’ nests were thy mercies extended," or, "For thy goodness be thy name remembered," or one who says twice, "Modim" [in the Amidah], he shall be silenced [by authority]. Also, whoever explains the text (Lev. 18:21), Umizaracho lo titen laehavir lamolech to mean, "Thou shalt not give thy seed to an Aramite [heathen] woman," and those who explain figuratively the section in the law relating to the prohibition of carnal intercourse between relatives (Lev. 18), shall be silenced, and publicly reprimanded.

(לג) וְכִֽי־יָג֧וּר אִתְּךָ֛ גֵּ֖ר בְּאַרְצְכֶ֑ם לֹ֥א תוֹנ֖וּ אֹתֽוֹ׃ (לד) כְּאֶזְרָ֣ח מִכֶּם֩ יִהְיֶ֨ה לָכֶ֜ם הַגֵּ֣ר ׀ הַגָּ֣ר אִתְּכֶ֗ם וְאָהַבְתָּ֥ לוֹ֙ כָּמ֔וֹךָ כִּֽי־גֵרִ֥ים הֱיִיתֶ֖ם בְּאֶ֣רֶץ מִצְרָ֑יִם אֲנִ֖י יְהוָ֥ה אֱלֹהֵיכֶֽם׃
(33) When a stranger resides with you in your land, you shall not wrong him. (34) The stranger who resides with you shall be to you as one of your citizens; you shall love him as yourself, for you were strangers in the land of Egypt: I the LORD am your God.
מיתיבי איזהו גר תושב כל שקיבל עליו בפני ג' חברים שלא לעבוד עבודת כוכבים דברי ר"מ וחכ"א כל שקיבל עליו שבע מצות שקבלו עליהם בני נח אחרים אומרים אלו לא באו לכלל גר תושב אלא איזהו גר תושב זה גר אוכל נבילות שקבל עליו לקיים כל מצות האמורות בתורה חוץ מאיסור נבילות
The Gemara raises an objection from a baraita: Who is a ger toshav? It is anyone who has accepted upon himself before three ḥaverim, i.e., people devoted to the meticulous observance of mitzvot, especially halakhot of ritual purity, teruma, and tithes, not to worship idols. This is the statement of Rabbi Meir. And the Rabbis say: Anyone who has accepted upon himself observance of the seven mitzvot that the descendants of Noah accepted upon themselves is a ger toshav. Others say: These have not entered the category of ger toshav. Rather, who is a ger toshav? This is a convert who eats unslaughtered animal carcasses, which are not kosher, but who has accepted upon himself to observe all of the mitzvot that are stated in the Torah except for the prohibition against eating unslaughtered carcasses.

(ז) גֵּר תּוֹשָׁב וְהוּא שֶׁקִּבֵּל עָלָיו שֶׁבַע מִצְוֹת כְּמוֹ שֶׁבֵּאַרְנוּ יֵינוֹ אָסוּר בִּשְׁתִיָּה וּמֻתָּר בַּהֲנָיָה. וּמְיַחֲדִין אֶצְלוֹ יַיִן וְאֵין מַפְקִידִין אֶצְלוֹ יַיִן. וְכֵן כָּל עַכּוּ''ם שֶׁאֵינוֹ עוֹבֵד עַכּוּ''ם כְּגוֹן אֵלּוּ הַיִּשְׁמְעֵאלִים יֵינָן אָסוּר בִּשְׁתִיָּה וּמֻתָּר בַּהֲנָיָה. וְכֵן הוֹרוּ כָּל הַגְּאוֹנִים. אֲבָל אוֹתָם הָעוֹבְדִים עַכּוּ''ם סְתַם יֵינָם אָסוּר בַּהֲנָיָה:

(7) A Ger Toshav -- He who has accepted the Seven Mitzvot of the sons of Noah, as we have explained -- it is prohibited to drink his wine, but it is permitted to derive benefit from it. And one may leave wine with him briefly, but not for a long time. And so too any Gentile who does not worship the stars and the constellations, such as the Ishmaelites, their wine may not be drunk, but one may derive benefit from it. And such instructed all the Geonim. But those who worship the stars and the constellations, one may not derive benefit from their wine.

Josephus, The Jewish War

[The Antiochian Jews] were constantly attracting to their religious ceremonies multitudes of Greeks, and these they had in some measure incorporated with themselves. But no one need wonder that there was so much wealth in our Temple, for all the Jews throughout the habitable world, and Yirei HaShem, even those from Asia and Europe, had been contributing to it for a very long time.

(ט) יִ֭שְׂרָאֵל בְּטַ֣ח בַּיהוָ֑ה עֶזְרָ֖ם וּמָגִנָּ֣ם הֽוּא׃ (י) בֵּ֣ית אַ֭הֲרֹן בִּטְח֣וּ בַיהוָ֑ה עֶזְרָ֖ם וּמָגִנָּ֣ם הֽוּא׃ (יא) יִרְאֵ֣י יְ֭הוָה בִּטְח֣וּ בַיהוָ֑ה עֶזְרָ֖ם וּמָגִנָּ֣ם הֽוּא׃ (יב) יְהוָה֮ זְכָרָ֪נוּ יְבָ֫רֵ֥ךְ יְ֭בָרֵךְ אֶת־בֵּ֣ית יִשְׂרָאֵ֑ל יְ֝בָרֵ֗ךְ אֶת־בֵּ֥ית אַהֲרֹֽן׃ (יג) יְ֭בָרֵךְ יִרְאֵ֣י יְהוָ֑ה הַ֝קְּטַנִּ֗ים עִם־הַגְּדֹלִֽים׃
(9) O Israel, trust in the LORD! He is their help and shield. (10) O house of Aaron, trust in the LORD! He is their help and shield. (11) O you who fear the LORD, trust in the LORD! He is their help and shield. (12) The LORD is mindful of us. He will bless us; He will bless the house of Israel; He will bless the house of Aaron; (13) He will bless those who fear the LORD, small and great alike.

Rabbi Tzvi Peres Chayes, Cheif Rabbi of Vienna, 1921

This is a clear proof, supporting what we know from Jewish-Hellenistic literature, that these PartialGentiles had a reserved section in the temple, apart from the sections for Israelites, Levites and Priests. This is a clear proof that they are not part of Israel but are foreigners, partial converts, who are Jewish according to the essence of their faith, and therefore present for Jewish worship

Mekhilta D'rebbe Yishmael, Exodus 22:20

One shall say: 'I am the L rd's'; another shall call in the name of Yaakov; another shall mark his arm 'of the L rd'; and in the name of Israel he shall be called": "I am the L rd's" — these are the fearers of Heaven, untainted by sin. "another shall call in the name of Yaakov" — these are the minors (who died in childhood), the sons of the wicked in Israel. "another shall mark his arm 'of the L rd'" — these are the penitents. "and in the name of Israel he shall be called — these are the righteous strangers (i.e., the proselytes).

Pesikta Rabbati

When Sarah gave birth to Isaac the nations of the world mocked her saying ‘He is the son of a servant and she pretends to be nursing him. At that time Abraham told Sarah ‘this is not a time for modesty. Present yourself for the sanctification of God’s name. Sarah exposed her breasts and milk came pouring out like springs of water as it is written there (Gen. 21) ‘Who would have told Abraham, Sarah would suckle sons.’.. The nations of the world brought their children to Sarah for breastfeeding...All converts in the world who join the Jewish community and all those who are Yirei HaShem in the world are from those who sucked from Sarah’s milk, hence it is written ‘The mother of the children is joyful.’ (Psalm 113) - this is Sarah

Yechaveh Da'at 4:55 (Rav Ovadia Yosef)

The sages forbade eating the bread of gentiles and idolaters. It seems that the gentiles in our lands who are Muslims and do not worship idols, it is permitted to eat their cooked foods and their bread, and so it seems from the words of the Sheikh, who noted what it says in Section 124:12, that Muslims render wine forbidden only for drinking, not for deriving benefit. What he means to say is that wine used for libations by idolaters is forbidden for drinking and deriving benefit, so the wine of Muslims is one level lower. If so, with their bread and cooked foods, which would ordinarily be forbidden only for eating, if they are not idolaters it is completely permitted.

Yabia Omer 5:10

The entirety of the prohibition against eating gentile bread is because of a concern about seclusion with a gentile woman, and [the concern about] seclusion with a gentile woman is in order to distance oneself from her idolatry. If this is so, it is clear that the decree [about bread] refers specifically to gentiles who perform idolatry, and not regarding gentiles who do not perform idolatry. If so, we have no reason to forbid the bread of Muslims, who disavow idolatry and hate idol-worshippers, and there is no decree about them.

Shulchan Ha'ma'arechet (Rabbi Yitzchak Yosef, son of Ovadia Yosef, current Sephardic cheif Rabbi of Israel)

Kiddushin are not effective with a non-Jewish woman, because it is written “do not make marriages with them [for doing so will turn away you son from following Me, that they may serve other gods].” But with a ger toshav woman, since there is no prohibition of “do not make marriages with them” [because they do not serve other gods], kiddushin are effective.

Rabbi Avigdor Nebenzahl (Israeli Orthodox Rabbi)

We find (Ruth 4:10) that the biblical Ruth, the wife of Mahlon, even when she was with him still had not converted. And it seems that she was a ger toshav, and so the law of marriage from “and he shall cling to his wife” applies, and so she was not included in the category of those who tempt [towards idolatry], even though the hold of Jewish kiddushin did not apply to her.