משנה על מעשר שני 3:1

One who has [second tithe] money in Jerusalem and he needs [to spend] it, and his friend had [non-sacred] produce, he may say to his friend: “Let this money be exchanged for your produce.” It turns out that the one [must] eat his produce in purity and the other may do what he needs with his money. But he may not say thus to an am haaretz except when [the money was] from [second tithe of] demai.

If [one had hullin] produce in Jerusalem and [second tithe money] in the provinces, he may say: “Let that money be exchanged for this produce.” If [he had second tithe] money in Jerusalem and [hullin] produce in the provinces, he may say: “Let this money be exchanged for that produce,” as long as he will carry that produce and eat it in Jerusalem.

[Second tithe] money may be brought into Jerusalem and taken out again, but [second tithe] produce may only be brought in, but not taken out again. Rabban Shimon ben Gamaliel says: produce also may be brought in and be taken out again.