We have indeed, likewise, a second font, (itself withal one with the former,) of blood, to wit; concerning which the Lord said, “I have to be baptized with a baptism,” when He had been baptized already. For He had come “by means of water and blood,” just as John has written; that He might be baptized by the water, glorified by the blood; to make us, in like manner, called by water, chosen by blood. These two baptisms He sent out from the wound in His pierced side, in order that they who believed in His blood might be bathed with the water; they who had been bathed in the water might likewise drink the blood. This is the baptism which both stands in lieu of the fontal bathing when that has not been received, and restores it when lost.
Reproduced in full. Translation: Ante-Nicene Fathers, vol. 3 (Roberts and Donaldson, 1885), public domain (Public domain).