Emor, Chapter 4
1) (Vayikra 22:4) ("A man, a man, of the seed of Aaron the Cohein, if he is a leper or a zav (see section 15), of the holy things he shall not eat until he is clean. And one who touches anyone who is unclean through the dead; or a man from whom semen issues,") "the seed of Aaron": This tells me only of the seed of Aaron. Whence is Aaron himself derived (as subsumed in the prohibition)? From "if he is a leper or a zav." "of the holy things (terumah) he shall not eat until he is clean": (i.e., when the sun goes down,) but Israelites may eat ma'aser t'vulei yom (having immersed themselves in the daytime). Whence is it derived that Aaron and his sons (may eat ma'aser, t'vulei yom)? It follows a fortiori, viz.: If Israelites, who may not eat of terumah (even) when the sun goes down, may eat of ma'aser t'vulei yom, then Aaron and his sons, who may eat of terumah when the sun goes down — how much more so may they eat of ma'aser t'vulei yom! Israelites, then, are derived (by implication) from the verse, and Aaron and his sons, a fortiori (as being permitted to eat ma'aser t'vulei yom.