Eliezer's Sign, the Mouser Rebbe, and Rabbi Meir Baal HaNes: Using Segulas in Judaism

Affectionately known as Reb Shaya'le (Rabbi Yeshaya Steiner of Kerestir), the Kerestirer Rebbe lived around the beginning of the 20th Century. He was a very pious man and extremely humble, always referring to himself in the diminutive (Shaya'le). He was known as a "miraculous" person. His greatest pleasure was to host a very elaborate Melave Malka, the meal that follows Shabbos, on Saturday night. Often he would have his chassidim shecht fresh chickens for his meal.

One motzo'ay Shabbos, while Reb Shaya'le was eating this special melave malka meal, a chossid came to him with an urgent request. He was a man who had a warehouse full of foodstuffs and he made his living by buying an selling food. For the past number of months, his warehouse had been taken over by mice who were eating his grain and other commodities and his entire livelihood was threatened. He asked Reb Shaya'le for a blessing that the mice should leave his warehouse. At that time, each small town in Europe was ruled by the local church pastor. Some of the pastors were kind towards the Jews and others were very harsh. Reb Shaya'le asked the chossid if the pastor of the town he lived in was kind or harsh. The chossid replied that he was very harsh toward the Jews. Reb Shaya'le then instructed the chossid to go to his warehouse and to tell the mice, "Reb Shaya'le says to go to the estate of the pastor." The chossid followed the Rebbe's advice and instantly hundreds of mice raced out of the warehouse all heading in the direction of the pastor's estate. The chossid's business was saved and ever since Jews who have been plagued with this problem have used Reb Shaya'le's picture to accomplish the ridding of mice from their homes. - Reb Shayele - Stories (jewishgen.org)

The story behind the segula of Rav Meir Baal HaNes has its basis in Mesechtes Avodah Zarah 18a-b of the Talmud.

When Rabbi Meir’s in-laws were found teaching Torah publicly, they were executed and his sister-in-law was taken by the Romans. Determined to win her release, Rabbi Meir took a large bag of golden dinars and approached her warden with the bribe. “Take the dinars, and give her to me!” he demanded. The warden, fully aware of his fate should the escape be discovered, refused. Rabbi Meir then instructed him that if his superiors would try to harm him, he need only cry out, “G-d of Meir, answer me!” and the threat would disappear. The warden was skeptical, so Rabbi Meir proved the efficacy of the segula by throwing a stone at the vicious jail dogs. When the dogs rushed to attack him, Rabbi Meir cried, “G-d of Meir, answer me!” and they retreated meekly. The Roman warden, satisfied that he could rely on the miracle, released the girl. Sure enough, her disappearance was quickly discovered, and the guard was taken to be hanged. At the last moment, he exclaimed, “G-d of Meir, answer me!” The executioner suddenly stopped, took him down from the gallows, and questioned him. When the guard revealed the entire episode, the Romans engraved a likeness of Rabbi Meir on the city gates and hunted him down as a wanted man. Rabbi Meir narrowly escaped, but felt it necessary to run away to Babylon to avoid the Romans. - Prayer for Lost Object | The Story Behind the Segula | Kupath Rabbi Meir Baal Hanes

(יב) וַיֹּאמַ֓ר ׀ ה' אֱלֹקֵי֙ אֲדֹנִ֣י אַבְרָהָ֔ם הַקְרֵה־נָ֥א לְפָנַ֖י הַיּ֑וֹם וַעֲשֵׂה־חֶ֕סֶד עִ֖ם אֲדֹנִ֥י אַבְרָהָֽם׃ (יג) הִנֵּ֛ה אָנֹכִ֥י נִצָּ֖ב עַל־עֵ֣ין הַמָּ֑יִם וּבְנוֹת֙ אַנְשֵׁ֣י הָעִ֔יר יֹצְאֹ֖ת לִשְׁאֹ֥ב מָֽיִם׃ (יד) וְהָיָ֣ה הַֽנַּעֲרָ֗ אֲשֶׁ֨ר אֹמַ֤ר אֵלֶ֙יהָ֙ הַטִּי־נָ֤א כַדֵּךְ֙ וְאֶשְׁתֶּ֔ה וְאָמְרָ֣ה שְׁתֵ֔ה וְגַם־גְּמַלֶּ֖יךָ אַשְׁקֶ֑ה אֹתָ֤הּ הֹכַ֙חְתָּ֙ לְעַבְדְּךָ֣ לְיִצְחָ֔ק וּבָ֣הּ אֵדַ֔ע כִּי־עָשִׂ֥יתָ חֶ֖סֶד עִם־אֲדֹנִֽי׃
(12) And he said, “O LORD, God of my master Abraham, grant me good fortune this day, and deal graciously with my master Abraham: (13) Here I stand by the spring as the daughters of the townsmen come out to draw water; (14) let the maiden to whom I say, ‘Please, lower your jar that I may drink,’ and who replies, ‘Drink, and I will also water your camels’—let her be the one whom You have decreed for Your servant Isaac. Thereby shall I know that You have dealt graciously with my master.”

אֵין מְנַחֲשִׁין כְּעַכּוּ''ם שֶׁנֶּאֱמַר (ויקרא יט כו) "לֹא תְנַחֲשׁוּ"... וְכֵן הַמֵּשִׂים סִימָנִים לְעַצְמוֹ אִם יֶאֱרַע לִי כָּךְ וְכָךְ אֶעֱשֶׂה דָּבָר פְּלוֹנִי וְאִם לֹא יֶאֱרַע לִי לֹא אֶעֱשֶׂה, כֶּאֱלִיעֶזֶר עֶבֶד אַבְרָהָם. וְכֵן כָּל כַּיּוֹצֵא בַּדְּבָרִים הָאֵלּוּ הַכּל אָסוּר. וְכָל הָעוֹשֶׂה מַעֲשֶׂה מִפְּנֵי דָּבָר מִדְּבָרִים אֵלּוּ לוֹקֶה:

It is forbidden to practice enchantment as the idolaters do, even as it is said: "Nor shall ye use enchantment" (Ibid. 19.26)... So, too, is one who sets certain signs for himself to regulate his actions, saying: "If such thing will come to pass I shall do that thing, but if it will not come to pass I shall not do it", even as Eliezer, Abrahams servant did. And so are all like practices of such things forbidden. And whosoever commits an act as a result of any one of such practices, is lashed.

וכן המשים לעצמו סימנים אם יארע לו כך וכך וכו'. א''א זה שבוש גדול שהרי דבר זה מותר ומותר הוא ואולי הטעהו הלשון שראה כל נחש שאינו כאליעזר ויונתן אינו נחש והוא סבר שלענין איסור נאמר ולא היא אלא ה''ק אינו ראוי לסמוך ואיך חשב על צדיקים כמותם עבירה זו ואי הוו אינהו הוו מפקי פולסי דנורא לאפיה:
So, too, is one who sets certain signs for himself etc. This is a gross error, for such thing is, indeed, permitted. Perhaps the text (Hullin, 95b) misled him, as he saw there, saying: "Such divination which is not like the divination of Eliezer (Gen. 24. 13–14) and Jonathan (I. Samuel, 20. 21–22) is not considered divining", and he evidently thought that the subject there is concerning a charge against such practice. Whereas it is not all so, for the meaning thereof is this: It is not proper to depend upon it. I wonder how he could think that way of such righteous men. Indeed, had they been present when he said it, they would have applied tongues of fire to his face.
וַיֹּ֨אמֶר ה' אֶל־מֹשֶׁ֗ה עֲשֵׂ֤ה לְךָ֙ שָׂרָ֔ף וְשִׂ֥ים אֹת֖וֹ עַל־נֵ֑ס וְהָיָה֙ כׇּל־הַנָּשׁ֔וּךְ וְרָאָ֥ה אֹת֖וֹ וָחָֽי׃
Then the LORD said to Moses, “Make a seraph figure and mount it on a standard. And if anyone who is bitten looks at it, he shall recover.”

וְכִי נָחָשׁ מֵמִית אוֹ מְחַיֶּה? אֶלָּא, בִּזְמַן שֶׁהָיוּ יִשְׂרָאֵל מִסְתַּכְּלִין כְּלַפֵּי מַעְלָה וּמְשַׁעְבְּדִין אֶת לִבָּם לַאֲבִיהֶם שֶׁבַּשָּׁמַיִם הָיוּ מִתְרַפְּאִים, וְאִם לָאו הָיוּ נִמּוֹקִים (ראש השנה כ"ט):

Our Rabbis said: But could the copper serpent cause death or life?! But the explanation is that when the Israelites in gazing at the serpent looked up on high and subjected their hearts to their Father in Heaven, they were healed, but if they did not do this they waste away (Rosh Hashanah 29a).

תָּנוּ רַבָּנַן: שִׁשָּׁה דְבָרִים עָשָׂה חִזְקִיָּהוּ הַמֶּלֶךְ, עַל שְׁלֹשָׁה הוֹדוּ לוֹ, וְעַל שְׁלֹשָׁה לֹא הוֹדוּ לוֹ. עַל שְׁלֹשָׁה הוֹדוּ לוֹ... כִּתֵּת נְחַשׁ הַנְּחשֶׁת — וְהוֹדוּ לוֹ...

The Sages taught: King Hezekiah performed six innovative actions. With regard to three the Sages agreed with him, and with regard to three they did not agree with him. With regard to three actions the Sages agreed with him...
He ground the copper snake through which miracles were performed for Israel (Numbers 21:9), destroying it because it had been used in idol worship (II Kings 18:4), and they agreed with him.