Mischna zu Dewarim 25:4

And it is also subject to tithes and poor man’s tithe. Both Israelites and priests that are poor may accept them, but the poor Israelites must sell that which is theirs to the priest for the price of terumah and the money belongs to them. He who beats the grain with sticks [instead of threashing with an animal] is to be praised. But he who threshes it [by having an animal walk on it] what should he do? He must suspend baskets from the neck of the animal and place in them from the same kind, with the result that he will neither muzzle the animal nor feed it terumah.