Parashas Metzora · Passuk 15:06
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “On the article” — I have only [learned the case] when he sits on it and the zav is there; from where [do we learn] to treat the empty [article] like the full? Scripture teaches “article.”
Empty midras like occupied
Chazal extend impurity to contact with the zav’s seat even when the zav is no longer sitting on it.