Augustine of Hippo
Catena Aurea · Johannesevangelium 13
Then cometh he to Simon Peter: and Peter said unto him, Lord, dost thou wash my feet? Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter. Peter saith unto him, Thou shalt never wash my feet. Jesus answered him, If I wash thee not, thou hast no part with me. Simon Peter saith unto him, Lord, not my feet only, but also my hands and my head. Jesus saith to him, He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean, but not all. For he knew who should betray him; therefore said he, Ye are not all clean. Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter.
(Ad. Seleuc. Ep. c. viii.) From what is here said, we understand that Peter was already baptized. Indeed that He baptized by His disciples, shews that His disciples must have been baptized, either with John’s baptism, or, which is more probable, Christ’s. He baptized by means of baptized servants; for He did not refuse the ministry of baptizing, Who had the humility to wash feet.