A.T. Robertson 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)

Thou shalt not muzzle (ου φιμωσεις). Prohibition by ου and future (volitive) indicative of φιμοω (from φιμος, muzzle), old word, quoted also in 1 Corinthians 9:9 as here from De 25:4, and for the same purpose, to show the preacher's right to pay for his work. See 1 Corinthians 9:9 for αλοωντα (when he treadeth out the corn ).

The labourer is worthy of his hire (αξιος ο εργατης του μισθου αυτου). These words occur in precisely this form in Lu 10:7. It appears also in Mt 10:10 with της τροφης (food) instead of του μισθου. In 1 Corinthians 9:14 Paul has the sense of it and says: "so also the Lord ordained," clearly meaning that Jesus had so said. It only remains to tell whether Paul here is quoting an unwritten saying of Jesus as he did in Ac 20:35 or even the Gospel of Luke or Q (the Logia of Jesus). There is no way to decide this question. If Luke wrote his Gospel before A.D. 62 as is quite possible and Acts by A.D. 63, he could refer to the Gospel. It is not clear whether Scripture is here meant to apply to this quotation from the Lord Jesus. For εργατης (labourer) see Php 3:2.