Мидраш к Бамидбар 18:29

1) (Vayikra 7:14) ("And he shall offer of it, one of each offering, a gift-offering (terumah) to the L–rd. To the Cohein who sprinkles the blood of the peace-offerings, to him shall it be.") "And he shall offer of it": of the conjoined loaves. "one": he must not take a broken one. "of each offering": All the offerings must be equal. (He may not take a greater portion of one on behalf of the other), and he may not take from one offering for the other. "terumah to the L–rd": I would not know from how many (challoth he takes one); it is, therefore, written here "terumoth," and, in respect to terumath ma'aser (Numbers 18:29) "terumah." Just as there, one of ten; here, too, one of ten.