Deuteronomy 25:4

לא תחסם שור THOU SHALT NOT MUZZLE THE OX [WHEN HE TREADETH OUT THE CORN] — Scripture is speaking of what usually occurs, but the same law applies to any cattle, non-domesticated beast and fowl that are doing some work that is connected with food. But if so why does it (Scripture) state “ox”? To exclude a human being from being subject to this law! (i.e. that if he restrains a workman from eating whilst engaged on some operation connected with food, the master is exempt from flagellation usually inflicted on one who transgresses a negative commandment) (Bava Metzia 88b). בדישו WHEN HE TREADETH OUT THE CORN — One might think that one might muzzle it previous to that (lit., outside, i.e., before it starts working)! Scripture, however, states, “thou shalt not muzzle an ox” — which implies thou shalt not muzzle it under any circumstances (Bava Metzia 90b). Then why is threshing mentioned?. In order to tell you the following: What is threshing? Its characteristic is that it is done on a thing the work on which is not yet complete to make it liable to tithing and the giving of Challah, and which grows from the ground. So, too, this prohibition applies only to all operations which have similar characteristics: Thus there are excluded from the prohibition “not to muzzle” (i.e. you may restrain from eating) workmen who are engaged in milking, in cheese-making, or in pressing the moisture out of thick milk, all of which operations are done on things which do not grow from the ground; there are excluded, also, the workmen who are engaged in kneading, or in breaking the dough up into pieces for baking, for the work on it is then completed so that it becomes liable to Challah. There are also excluded the workmen engaged in separating dates and figs from the mass, for the work on them is then completed so that they become liable to tithing (Bava Metzia 89a).

לֹא־תַחְסֹ֥ם שׁ֖וֹר בְּדִישֽׁוֹ׃ {ס}        

Thou shalt not muzzle the ox when he treads out the corn.