Reference for Leviticus 15:6

וְהַיֹּשֵׁב֙ עַֽל־הַכְּלִ֔י אֲשֶׁר־יֵשֵׁ֥ב עָלָ֖יו הַזָּ֑ב יְכַבֵּ֧ס בְּגָדָ֛יו וְרָחַ֥ץ בַּמַּ֖יִם וְטָמֵ֥א עַד־הָעָֽרֶב׃

And he that sitteth on any thing whereon he that hath the issue sat shall wash his clothes, and bathe himself in water, and be unclean until the even.