פירוש על עבודה זרה 92:12

The problem with Mar Zutra is that he assumes that the dispute occurs when the animal first became pregnant and then was subject to bestiality. But R. Nahman says there is no dispute in this case, for in this case the offspring was conceived when the animal was already prohibited. So too in the case of the standing-grain it was prohibited before the flour was “born.” Thus all should agree that it is prohibited for use on the altar.