Augustine says (Ep. cclxv), from our Lord's words:
'He that is washed, needeth not but to wash his feet' (John 13:10), we gather that Peter and Christ's other disciples had been baptized, either with John's Baptism, as some think; or with Christ's, which is more credible. For He did not refuse to administer Baptism, so as to have servants by whom to baptize others.
Quoted from St. Thomas Aquinas' Summa theologiae III, q. 72, a. 6, ad. 2)