利未记 15:6

והישב על הכלי AND HE THAT SITTETH ON ANY THING [WHEREON HE SAT THAT HATH AN ISSUE … SHALL BE UNCLEAN] — even though he (the person) is not actually in contact with it: even if there be ten things one upon the other, the lowest being that upon which a זב has once sat, they all communicate uncleanness according to the law applicable to a seat upon which an unclean person has sat, and similarly is the case with an object upon which he has lain (cf. Sifra, Metzora Parashat Zavim, Chapter 3 1).

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

And he that sits on anything on which he that has the issue sat, shall wash his clothes, and bathe himself in water, and be unclean until evening.