וּמָכַרְתִּ֞י אֶת־בְּנֵיכֶ֣ם וְאֶת־בְּנֽוֹתֵיכֶ֗ם בְּיַד֙ בְּנֵ֣י יְהוּדָ֔ה וּמְכָר֥וּם לִשְׁבָאיִ֖ם אֶל־גּ֣וֹי רָח֑וֹק כִּ֥י יְהוָ֖ה דִּבֵּֽר׃ (ס)
Rashi on Joel
for the Lord has spoken—Now where did He speak? (Gen. 9:25) “A slave of slaves shall he be to his brothers.” So it is explained in Mechilta (Ex. 12:25).