From the First Epistle of Peter
See with what earnestness the apostles declare this doctrine, when they received it. Peter, in his first Epistle, says: “Blessed be the God and Father of our Lord Jesus Christ, according to His abundant mercy, who has regenerated us unto the hope of eternal life, by the resurrection of Jesus Christ, to an inheritance immortal, and undefiled, flourishing, reserved in heaven for you, who are kept by the power of God through faith unto salvation, ready to be revealed in the last time.” And a little afterwards he adds: “May you be found unto the praise and honour of Jesus Christ: of whom you were ignorant; but in whom you believe, though now you see Him not; and in whom also you shall rejoice, when you shall see Him, with joy unspeakable and full of glory: receiving the end of your faith, even the salvation of your souls.” Again, in another place he says: “But you are a chosen generation, a royal priesthood, a holy nation, a peculiar people; that you should show forth the praises of Him who has called you out of darkness into His marvellous light.” Once more he says: “Christ has once suffered for our sins, the just for the unjust, that He might bring us to God:” and, after mentioning the fact of eight persons having been saved in Noah's ark, he adds: “And by the like figure baptism saves you.” Now infants are strangers to this salvation and light, and will remain in perdition and darkness, unless they are joined to the people of God by adoption, holding to Christ who suffered the just for the unjust, to bring them unto God.
Source: Merits and Remission of Sin, and Infant Baptism (New Advent)