משנה אויף ויקרא 27:23

One may clear away even four or five baskets of straw or produce to make room for guests or on account of the neglect of the study hall, but not the storehouse. One may clear away pure terumah, doubtfully tithed produce, the first tithe whose terumah has been separated, redeemed second tithe and sanctified things, and dry lupinus, because it is food for goats. But [one may] not [clear away] untithed produce, first tithe whose terumah has not been taken, unredeemed second tithe and sanctified things, luf or mustard. Rabban Shimon b. Gamaliel permits [it] in the case of luf, because it is food for ravens.