Tertullian, On Baptism 8

Then the hand is placed, through blessing calling and inviting the Holy Spirit. Indeed, human ingenuity permits summoning a spirit into the water and animating their incorporation with another spirit of such great clarity, by placing hands from above; but will God not be permitted, in His own instrument, to modulate spiritual sublimity through holy hands? This, too, belongs to the old sacrament by which Jacob blessed his grandchildren from Joseph, Ephraim and Manasseh, with hands imposed on their heads and crossed—in such a way that, by deforming Christ, they then already portended the future blessing in Christ (Genesis 48:14). Then that most holy Spirit descends willingly from the Father upon purified and blessed bodies, upon the waters of Baptism, as if recognizing a former seat; He rests, having fallen in the form of a dove upon the Lord, so that the nature of the Holy Spirit might be declared through an animal of simplicity and innocence, which also corporally lacks bile. And therefore: 'Be simple as doves,' He says—not even this without a precedent figure. For just as after the flood waters, by which ancient iniquity was purged, after Baptism (so to speak) the dove announced to the earth the peace of heavenly wrath, dismissed from the ark and returning with an olive branch—which sign is also held out to nations for peace—by the same disposition the dove of the Holy Spirit flies to the spiritual effect upon the earth, that is, our flesh emerging from the washing after former sins, bringing the peace of God, sent from the heavens where the Church is figured as the ark. But the world sins again, by which Baptism is compared unfavorably to the flood. And so it is destined for fire, just as the man who after Baptism restores sins, so that this also ought to be taken as a sign of our admonition.