Augustine of Hippo — as excerpted in the Catena Aurea on John 13:12-20

“(Tr. lviii. 2) Our Lord, mindful of His promise to Peter that he should know the meaning of His act, Thou shalt know hereafter, now begins to teach him: So after He had washed their feet, and had taken His garments, and was sat down again, He said unto them, Know ye what I have done to you?”