הלכה אויף במדבר 18:12

One may make an eruv or make a shituf with food that is permissible to eat, even though it is forbidden to the one making the eruv. How is this? A nazerite may make a shituf with wine, and an Israelite [may do so] with priestly tithe. And likewise one who has made a vow from eating this, or sworn not to eat it, may make an eruv with it or make a shituf with it. For [even] if it is not fit for this one, it is fit for another.

Priests (kohanim) fulfill [their obligation] with challah-tithe and with priestly tithe, even though it is matsa that is not fit for everyone. And likewise do we fulfill our obligation with second tithe in Jerusalem. But we do not fulfill [our obligation] with matsa of the first fruits (bikkurim) - even in Jerusalem. For first fruits are not permitted in all settlements; whereas [with] second tithe, it is possible that he will redeem [it] and eat [it] in any place. And it is written, (Exodus 12:20), "you shall eat matsas in all of your settlements" - matsa that is fit to be eaten in all of the settlements is the one with which we fulfill our obligation.

A citron of the first three years or of impure priestly tithe or untithed produce is disqualified. [If it is] of demai, it is fit — since it is possible that he would abandon his possessions and become a poor person, who is permitted to eat demai. One should not lift up a citron of pure priestly tithe or second tithe in Jerusalem, lest he make it fit for impurity. But if the lifted it up, it is fit.