[If] one imposes a vow on his fellow that he should eat with him, and [his fellow] does not trust him regarding tithes, he may eat with him on the first Sabbath, even though he does not trust [the host] regarding tithes, provided that [the host] says to him: ‘‘[The food] is tithed.’’ But on the second Sabbath, even though [the host] vowed that [his fellow] not have ben-efit from him, he may not eat unless he separates the tithes.

R’ Eliezer says: One does not need to verbally designate maasar ani from demai. But the Sages say: One verbally designates [it], but he does not need to separate [it].