Albert Barnes Commentary 1 Timothy 5:18

"For the scripture saith, Thou shalt not muzzle the ox when he treadeth out the corn. And, The laborer is worthy of his hire." — 1 Timothy 5:18 (ASV)

For the Scripture saith. This is cited as a reason why a church should show all due respect and care for its ministers. The reason is that, as God took care to make provision for the labouring ox, much more should due attention be paid to those who labour for the welfare of the church.

Thou shalt not muzzle the ox. See this passage explained, and its bearing on such an argument shown, in the comments on 1 Corinthians 9:8.

See also the comments on 1 Corinthians 9:9 and 1 Corinthians 9:10.

And, The labourer is worthy of his reward. This expression is found substantially in Matthew 10:10 and Luke 10:7. It does not occur in so many words in the Old Testament, and yet the apostle cites it evidently as a quotation from the Scriptures and as authority in the case. It would seem probable, therefore, that he had seen the Gospel by Matthew or by Luke. He quoted this as a part of Scripture and regarded the Book from which he made the quotation as having the same authority as the Old Testament. If so, then this may be regarded as an attestation by the apostle to the inspiration of the Gospel in which it was found.