Justin Martyr, on Isa 1:18

As many as are persuaded and believe that what we teach and say is true, and undertake to be able to live accordingly, are instructed to pray and to entreat God with fasting, for the remission of their sins that are past, we praying and fasting with them. Then they are brought by us where there is water, and are regenerated in the same manner in which we were ourselves regenerated. For, in the name of God, the Father and Lord of the universe, and of our Saviour Jesus Christ, and of the Holy Spirit, they then receive the washing with water. For Christ also said, "Except ye be born again, ye shall not enter into the kingdom of heaven." Now, that it is impossible for those who have once been born to enter into their mothers' wombs, is manifest to all. And how those who have sinned and repent shall escape their sins, is declared by Esaias the prophet, as I wrote above; he thus speaks: "Wash you, make you clean; put away the evil of your doings from your souls; learn to do well; judge the fatherless, and plead for the widow: and come and let us reason together, saith the Lord. And though your sins be as scarlet, I will make them white like wool; and though they be as crimson, I will make them white as snow. But if ye refuse and rebel, the sword shall devour you: for the mouth of the Lord hath spoken it."