Reference for Chullin 271:38

ראשית הגז אין נוהג אלא בארץ

What is R'Ila'i's reason? - Rab answered: He draws an analogy by means of the common expression 'giving' from terumah; as terumah obtains in the Land only and not outside it, so the law of the first of the fleece obtains in the Land only and not outside it.

Jastrow