YK ~ Kayin as baal teshuvah

הָאוֹמֵר, אֶחֱטָא וְאָשׁוּב, אֶחֱטָא וְאָשׁוּב, אֵין מַסְפִּיקִין בְּיָדוֹ לַעֲשׂוֹת תְּשׁוּבָה. אֶחֱטָא וְיוֹם הַכִּפּוּרִים מְכַפֵּר, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אֶת זוֹ דָּרַשׁ רַבִּי אֶלְעָזָר בֶּן עֲזַרְיָה, מִכֹּל חַטֹּאתֵיכֶם לִפְנֵי ה' תִּטְהָרוּ (ויקרא טז), עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אָמַר רַבִּי עֲקִיבָא, אַשְׁרֵיכֶם יִשְׂרָאֵל, לִפְנֵי מִי אַתֶּם מִטַּהֲרִין, וּמִי מְטַהֵר אֶתְכֶם, אֲבִיכֶם שֶׁבַּשָּׁמַיִם, שֶׁנֶּאֱמַר (יחזקאל לו), וְזָרַקְתִּי עֲלֵיכֶם מַיִם טְהוֹרִים וּטְהַרְתֶּם. וְאוֹמֵר (ירמיה יז), מִקְוֵה יִשְׂרָאֵל ה', מַה מִּקְוֶה מְטַהֵר אֶת הַטְּמֵאִים, אַף הַקָּדוֹשׁ בָּרוּךְ הוּא מְטַהֵר אֶת יִשְׂרָאֵל:

Mishnah Yoma 8:9

One who says, "I will sin, and then repent, I will sin [again], and then repent," will not receive an opportunity to repent; [for one who says] "I will sin, and Yom Kipur will atone," Yom Kippur will not atone. Yom Kippur atones for transgressions between a person and God, but for a transgression against one's neighbor, Yom Kipur cannot atone, until he appeases his neighbor. Thus R. Eleazar ben Azariah expounds the text, "From all your sins before the Lord shall ye be clean": For transgressions between a person and God, Yom Kippur atones, for transgressions against one's neighbor, Yom Kippur cannot atone, until he appeases his neighbor. R. Akiva says, Happy are you, Israel! Before whom are you purified, and who purifies you [of your transgressions]? Your Father Who is in heaven. For it is said, "Then will I sprinkle clean water upon you, and ye shall be clean"; and it is also said, "The ‏ritual bath‎ [lit. Hope] of Israel is the Lord"; even as a ritual bath purifies the unclean, so does the Holy One, Blessed be He, purify Israel.

בראשית ד׳:ג׳-ט״ז

(ג) וַֽיְהִ֖י מִקֵּ֣ץ יָמִ֑ים וַיָּבֵ֨א קַ֜יִן מִפְּרִ֧י הָֽאֲדָמָ֛ה מִנְחָ֖ה לַֽה'׃ (ד) וְהֶ֨בֶל הֵבִ֥יא גַם־ה֛וּא מִבְּכֹר֥וֹת צֹאנ֖וֹ וּמֵֽחֶלְבֵהֶ֑ן וַיִּ֣שַׁע ה' אֶל־הֶ֖בֶל וְאֶל־מִנְחָתֽוֹ׃ (ה) וְאֶל־קַ֥יִן וְאֶל־מִנְחָת֖וֹ לֹ֣א שָׁעָ֑ה וַיִּ֤חַר לְקַ֙יִן֙ מְאֹ֔ד וַֽיִּפְּל֖וּ פָּנָֽיו׃ (ו) וַיֹּ֥אמֶר ה' אֶל־קָ֑יִן לָ֚מָּה חָ֣רָה לָ֔ךְ וְלָ֖מָּה נָפְל֥וּ פָנֶֽיךָ׃ (ז) הֲל֤וֹא אִם־תֵּיטִיב֙ שְׂאֵ֔ת וְאִם֙ לֹ֣א תֵיטִ֔יב לַפֶּ֖תַח חַטָּ֣את רֹבֵ֑ץ וְאֵלֶ֙יךָ֙ תְּשׁ֣וּקָת֔וֹ וְאַתָּ֖ה תִּמְשָׁל־בּֽוֹ׃ (ח) וַיֹּ֥אמֶר קַ֖יִן אֶל־הֶ֣בֶל אָחִ֑יו וַֽיְהִי֙ בִּהְיוֹתָ֣ם בַּשָּׂדֶ֔ה וַיָּ֥קָם קַ֛יִן אֶל־הֶ֥בֶל אָחִ֖יו וַיַּהַרְגֵֽהוּ׃ (ט) וַיֹּ֤אמֶר ה' אֶל־קַ֔יִן אֵ֖י הֶ֣בֶל אָחִ֑יךָ וַיֹּ֙אמֶר֙ לֹ֣א יָדַ֔עְתִּי הֲשֹׁמֵ֥ר אָחִ֖י אָנֹֽכִי׃ (י) וַיֹּ֖אמֶר מֶ֣ה עָשִׂ֑יתָ ק֚וֹל דְּמֵ֣י אָחִ֔יךָ צֹעֲקִ֥ים אֵלַ֖י מִן־הָֽאֲדָמָֽה׃ (יא) וְעַתָּ֖ה אָר֣וּר אָ֑תָּה מִן־הָֽאֲדָמָה֙ אֲשֶׁ֣ר פָּצְתָ֣ה אֶת־פִּ֔יהָ לָקַ֛חַת אֶת־דְּמֵ֥י אָחִ֖יךָ מִיָּדֶֽךָ׃ (יב) כִּ֤י תַֽעֲבֹד֙ אֶת־הָ֣אֲדָמָ֔ה לֹֽא־תֹסֵ֥ף תֵּת־כֹּחָ֖הּ לָ֑ךְ נָ֥ע וָנָ֖ד תִּֽהְיֶ֥ה בָאָֽרֶץ׃ (יג) וַיֹּ֥אמֶר קַ֖יִן אֶל־ה' גָּד֥וֹל עֲוֺנִ֖י מִנְּשֹֽׂא׃ (יד) הֵן֩ גֵּרַ֨שְׁתָּ אֹתִ֜י הַיּ֗וֹם מֵעַל֙ פְּנֵ֣י הָֽאֲדָמָ֔ה וּמִפָּנֶ֖יךָ אֶסָּתֵ֑ר וְהָיִ֜יתִי נָ֤ע וָנָד֙ בָּאָ֔רֶץ וְהָיָ֥ה כָל־מֹצְאִ֖י יַֽהַרְגֵֽנִי׃ (טו) וַיֹּ֧אמֶר ל֣וֹ ה' לָכֵן֙ כָּל־הֹרֵ֣ג קַ֔יִן שִׁבְעָתַ֖יִם יֻקָּ֑ם וַיָּ֨שֶׂם ה' לְקַ֙יִן֙ א֔וֹת לְבִלְתִּ֥י הַכּוֹת־אֹת֖וֹ כָּל־מֹצְאֽוֹ׃ (טז) וַיֵּ֥צֵא קַ֖יִן מִלִּפְנֵ֣י ה' וַיֵּ֥שֶׁב בְּאֶֽרֶץ־נ֖וֹד קִדְמַת־עֵֽדֶן׃

Genesis 4:3-16

(3) In the course of time, Cain brought an offering to the LORD from the fruit of the soil; (4) and Abel, for his part, brought the choicest of the firstlings of his flock. The LORD paid heed to Abel and his offering, (5) but to Cain and his offering He paid no heed. Cain was much distressed and his face fell. (6) And the LORD said to Cain, “Why are you distressed, And why is your face fallen? (7) Surely, if you do right, There is uplift. But if you do not do right Sin couches at the door; Its urge is toward you, Yet you can be its master.” (8) Cain said to his brother Abel … and when they were in the field, Cain set upon his brother Abel and killed him. (9) The LORD said to Cain, “Where is your brother Abel?” And he said, “I do not know. Am I my brother’s keeper?” (10) Then He said, “What have you done? Hark, your brother’s blood cries out to Me from the ground! (11) Therefore, you shall be more cursed than the ground, which opened its mouth to receive your brother’s blood from your hand. (12) If you till the soil, it shall no longer yield its strength to you. You shall become a ceaseless wanderer on earth.” (13) Cain said to the LORD, “My punishment is too great to bear! (14) Since You have banished me this day from the soil, and I must avoid Your presence and become a restless wanderer on earth—anyone who meets me may kill me!” (15) The LORD said to him, “I promise, if anyone kills Cain, sevenfold vengeance shall be taken on him.” And the LORD put a mark on Cain, lest anyone who met him should kill him. (16) Cain left the presence of the LORD and settled in the land of Nod, east of Eden.

בראשית רבה כ״ב:י״ג

(יג) וַיֵּצֵא קַיִן מִלִּפְנֵי ה' (בראשית ד, טז), מֵהֵיכָן יָצָא, רַבִּי יוּדָן בְּשֵׁם רַבִּי אַיְבוּ אָמַר הִפְשִׁיל דְּבָרִים לַאֲחוֹרָיו וְיָצָא, כְּגוֹנֵב דַּעַת הָעֶלְיוֹנָה. רַבִּי בֶּרֶכְיָה בְּשֵׁם רַבִּי אֶלְעָזָר בְּרַבִּי שִׁמְעוֹן אָמַר, יָצָא כְּמַפְרִיס וְכִמְרַמֶּה בְּבוֹרְאוֹ. רַבִּי חָמָא בְּשֵׁם רַבִּי חֲנִינָא בַּר רַבִּי יִצְחָק אָמַר, יָצָא שָׂמֵחַ, הֵיךְ מָה דְאַתְּ אָמַר (שמות ד, יד): הִנֵּה הוּא יֹצֵא לִקְרָאתֶךָ וגו', פָּגַע בּוֹ אָדָם הָרִאשׁוֹן אָמַר לוֹ מַה נַּעֲשָׂה בְּדִינְךָ, אָמַר לוֹ עָשִׂיתִי תְּשׁוּבָה וְנִתְפַּשַּׁרְתִּי. הִתְחִיל אָדָם הָרִאשׁוֹן מְטַפֵּחַ עַל פָּנָיו, אָמַר, כָּךְ הִיא כֹּחָהּ שֶׁל תְּשׁוּבָה וַאֲנִי לֹא הָיִיתִי יוֹדֵעַ, מִיָּד עָמַד אָדָם הָרִאשׁוֹן וְאָמַר (תהלים צב, א): מִזְמוֹר שִׁיר לְיוֹם הַשַּׁבָּת וגו'. אָמַר רַבִּי לֵוִי הַמִּזְמוֹר הַזֶּה אָדָם הָרִאשׁוֹן אֲמָרוֹ וְנִשְׁתַּכַּח מִדּוֹרוֹ וּבָא משֶׁה וְחִדְּשׁוֹ עַל שְׁמוֹ, מִזְמוֹר שִׁיר לְיוֹם הַשַּׁבָּת טוֹב לְהוֹדוֹת לַה' וגו'.

Bereshit Rabbah 22:13

'And Kayin went out from the presence of Ad-nai' (Gen. 4:16) - from where did he go?! Rabbi Yudan in the name of Rabbi Ayvu said: he threw words behind him and went out, as one who could deceive the Highest Awareness. Rabbi Berachia in the name of Rabbi Eleazar son of Rabbi Shime'on said: he went out as one who shows the cloven hoof [a hypocrite] as one who deceives His Creator. Rabbi Chama in the name of Rabbi Chanina bar Rabbi Yitzchak said: he went out happy, as you read "behold he comes out to greet you [and when he sees you he'll be glad in his heart]" (Ex. 4:14). Adam met him and said: 'how did your judgement go?' and he answered: 'I repented [did teshuvah] and I am reconciled.' Adam began to hide his face [crying] and said: this is the power of teshuvah [repentance] and I did not know. Immediately Adam rose and said: 'A Psalm of Shabbat etc.' (Ps. 92) Said Rabbi Levi: this mizmor was said by the first Adam and it was forgotten in his generation, and came Moshe and renewed it under his name, 'it is a good thing to thank Ad-nai' (Ps. 92:1-2).

ונתנה תוקף ב׳

אֱמֶת כִּי אַתָּה הוּא דַּיָּן וּמוֹכִיחַ וְיוֹדֵעַ וָעֵד וְכוֹתֵב וְחוֹתֵם וְסוֹפֵר וּמוֹנֶה וְתִזְכֹּר כָּל הַנִּשְׁכָּחוֹת וְתִפְתַּח אֶת סֵפֶר הַזִּכְרוֹנוֹת וּמֵאֵלָיו יִקָּרֵא וְחוֹתָם יַד כָּל אָדָם בּוֹ

Unetaneh Tokef 2

It is true that you are the one who judges, and reproves, who knows all, and bears witness, who inscribes, and seals, who reckons and enumerates. You remember all that is forgotten. You open the book of records, and from it, all shall be read. In it lies each person's insignia.