פירוש על ויקרא 15:23

ואם על המשכב הוא AND IF ONE BE ON HER PLACE OF REPOSE [OR ON ANY THING WHEREON SHE SITTETH] — This means, one who sleeps or sits on the place where she has slept or has sat even though he does not directly touch it (e. g. if there are covers upon the couch or the seat; for if he touches it vv. 21 and 22 apply); he also comes under the law of uncleanness that is stated in the above verse — that he requires washing of garments.

'ואם על המשכב הוא וגו, if some sits or lies on something even indirectly in contact, מדרס, with the afflicted person chair or bed, etc., he will still become ritually contaminated by such indirect contact בנגעו בו יטמא עד הערב, even if the “contact” was so indirect as instead of sitting on the contaminated item one sat on a saddle supported by the contaminated item, the ritual impurity lasts until evening when immersion in a ritual bath removes it. He is then, however, not of a sufficiently severe degree of ritual impurity to contaminate clothing (even his own) over and beyond his body. In other words, in this kind of scenario the Torah did not add that he has to wash (immerse) his garments in order to become ritually pure again. (as it had done in verse 21 and 22, for instance)

Even if he did not touch [it]. This is as Rashi explains above (v. 6) regarding: “Whoever sits on the vessel” — “even if he did not touch [it].” Above (ibid.), I explained Rashi’s proofs that lying down and sitting cause impurity even though he does not touch the vessel. Rashi’s view is thus: Do not think that [the phrase] “when he touches it he shall be impure until the evening,” which it says after [the phrase], “If he is on the bed...” implies that even if he touches the bed, chair, or saddle he does not require washing clothes, and the explanation of the word “it” would be: “in each one of them.” This cannot be, for it does not refer to “If he is on the bed...” This is because even if he does not touch it he requires washing clothes. We need not ask: To what does the phrase “when he touches it he shall be impure until the evening” refer? Therefore Rashi explains: “On the vessel — to include...” I.e., why does it need to say, “on the vessel”? It only needs to say, “that she is sitting on.” Rather [it must be]: “To include a saddle.” If so, that which is written, “when he touches it...” refers to a saddle, as Rashi explains later that it does not require washing clothes.