Deuteronomy 25:4

The leaving the ox unmuzzled when treading out the corn was in order that the animal might be free to eat of the grains which its labor severed from the husks. This prohibition, therefore, was dictated by a regard to the rights and claims of animals employed in labor; but there is involved in it the general principle that all labor is to be duly requited, and hence it seems to have passed into a proverb, and was applied to men as well as the lower animals (cf. 1 Corinthians 9:9 ; 1 Timothy 5:18 ). The use of oxen to tread out the corn and the rule of leaving the animals so employed unmuzzled still prevail among the Arabs and other Eastern peoples.