3 Furthermore, we have read to them the work of the most blessed martyr Cyprian on the Lord's Prayer, and have pointed out to them how He taught that all things pertaining to our morals, which constitute right living, must be sought from our Father which is in heaven, test, by presuming on free will, we fall from divine grace. From the same treatise we have also shown them how the same glorious martyr has taught us that it behooves us to pray even for our enemies who have not yet believed in Christ, that they may believe; which would of course be all in vain unless the Church believed that even the evil and unbelieving wills of men might, by the grace of God, be converted to good. This book of St. Cyprian, however, we have not sent you, because they told us that you possessed it among yourselves already. My letter, also, which had been sent to Sixtus, presbyter of the Church at Rome? And which they brought with them to us, we read over with them, and pointed out how that it had been written in opposition to those who say that God's grace is bestowed according to our merits,--that is to say, in opposition to the same Pelagians.
Source: Letters (New Advent)