"And a man wrestled with him" (Genesis 32:25). The angel said to him: Did you not say (Genesis 28:22), "I will surely tithe to You"? Immediately Jacob took all his livestock and tithed from them five hundred and fifty. From here you learn that all his livestock numbered five thousand five hundred. The angel said to him: Behold, you have sons, and you did not tithe them. What did Jacob do? He set aside the four firstborn of the four mothers, and eight remained. He began with Simeon and finished with Benjamin, who was still in his mother's womb, and then he began again from Simeon, and Levi came up as the holy tithe, as it is said, "the tenth shall be holy" (Leviticus 27:32).
Jacob Tithes His Flocks and Sons and Levi Is Set Apart
Yalkut Shimoni on Torah 132:5
וַיֵּאָבֵק אִישׁ עִמּוֹ. אָמַר לוֹ הַמַּלְאָךְ, לֹא כַּךְ אָמַרְתָּ(י) (בראשית כח, כב) "עַשֵּׂר אֲעַשְּׂרֶנּוּ לָךְ", מִיַד לָקַח כָּל מִקְנֵהוּ וְעִשֵּׂר מֵהֶן חָמֵשׁ מֵאוֹת וַחֲמִשִּׁים מִכָּאן אַתָּה לָמֵד שֶׁכָּל מִקְנֵהוּ חֲמֵשׁ אֲלָפִים וַחֲמֵשׁ מֵאוֹת. אָמַר לוֹ הַמַּלְאָךְ, הֲרֵי יֵשׁ לְךָ בָּנִים וְלֹא עִשַּׂרְתָּ אוֹתָם. מֶה עָשָׂה יַעֲקֹב, הִפְרִישׁ אַרְבַּע בְּכוֹרוֹת לְאַרְבַּע אִמָּהוֹת וְנִשְׁתַּיְּרוּ שְׁמֹנָה, וְהִתְחִיל מִשִּׁמְעוֹן וְגָמַר בְּבִנְיָמִין שֶׁבִּמְעֵי אִמּוֹ, וְעוֹד הִתְחִיל מִשִּׁמְעוֹן וְעָלָה לֵוִי מַעֲשֵׂר קֹדֶשׁ, שֶׁנֶּאֱמַר "הָעֲשִׂירִי יִהְיֶה קֹּדֶשׁ".