Rashi on Leviticus 15:10/רש"י על ויקרא ט״ו:י׳

1וכל הנגע בכל אשר יהיה תחתיו AND WHOSOEVER TOUCHETH ANYTHING THAT WAS תחתיו — under the זב. This intends to teach regarding such an object for riding upon (if a זב has ridden on it) that whoever touches it becomes unclean, but he does not require washing of clothes and this is something stricter in the case of a thing for sleeping on than in that of a thing for riding on (since the former necessitates that his garments should be washed; cf. v. 5).

2והנושא אותם AND HE THAT BEARETH THEM — “them” means all that have been mentioned in the matter of a זב — his flow, his spittle, his semen, and his urine, and that upon which he has slept or ridden — the bearing of them makes a man unclean so that he in turn makes his garments unclean (cf. Sifra, Metzora Parashat Zavim, Chapter 4 4).