Saint Augustine 
On the Spirit and the Letter 

The person to whom I had addressed the three books entitled De Peccatorum Meritis et Remissione, in which I carefully discussed also the baptism of infants, informed me, when acknowledging my communication, that he was much disturbed because I declared it to be possible that a man might be without sin, if he wanted not the will, by the help of God, although no man either had lived, was living, or would live in this life so perfect in righteousness.