1 Corinthians 9:9

For it is written in the law of Moses, Thou shalt not muzzle the ox when he treadeth out the corn. Is it for the oxen that God careth,

'For it is written'. Deuteronomy 25:4

'Is it for the oxen that God careth' -'Do you think God was thinking only about oxen when He said this' (Tay). Now the Scriptures do teach that God 'cares' for the animal creation (Matthew 6:26 ff; Luke 12:22 ff; Matthew 12:11). And yet Paul argues, as did Jesus, that if God cares even for animals, He cares for people more!

'The text reflects the ancient agricultural practice of driving an ox drawing. threshing-sledge over the grain to release the kernels from the stalk. Out of mercy for the laboring animal the Israelites were forbidden to muzzle the ox, so that he might have some "material benefit" from his labor.' (Fee pp. 406-407)

And if God doesn't want the labor of an ox to go unrewarded, how much more the labor of. man!