1 Corinthians 9:8
“Do I speak these things after the manner of men? Or says not the law also the same?”
For since he had hitherto alleged nothing out of the Scriptures, but put forward the common custom; “think not,” says he, “that I am confident in these alone, nor that I go to the opinions of men for the ground of these enactments. For I can show that these things are also well-pleasing to God, and I read an ancient law enjoining them.” Wherefore also he carries on his discourse in the form of a question, which is apt to be done in things fully acknowledged; thus saying, “Say I these things after the manner of men?” i.e. “do I strengthen myself only by human examples?” “or says not the law also the same?”
Source: Homilies on First Corinthians (New Advent)