Parashas Metzora · Passuk 14:37
Chabad.org — English translation + Rashi
Torah Temima points to Nazir 8b (verified on the daf).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: “In the walls of the house” — the Sages taught: A round house, a digon, a trigon, or a pentagon does not become tamei through negaim; a tetragon does become tamei through negaim. Why? Below it says “wall / walls” and above it says “wall / walls” — here are four.
Requirement of four walls
Chazal require a four-walled (rectangular) structure; houses with fewer or more than four walls are exempt from house-nega laws.