Sifrei_mitzvot for Deuteronomy 21:12

וַהֲבֵאתָ֖הּ אֶל־תּ֣וֹךְ בֵּיתֶ֑ךָ וְגִלְּחָה֙ אֶת־רֹאשָׁ֔הּ וְעָשְׂתָ֖ה אֶת־צִפָּרְנֶֽיהָ׃

then thou shalt bring her home to thy house; and she shall shave her head, and pare her nails;