Augustine of Hippo

Perplexity may be occasioned to some by the great difference, not in words only, but in substance, of the speeches in which Peter is forewarned by Our Lord, and which occasion his presumptuous declaration of dying with or for the Lord. Some would oblige us to understand that he thrice expressed his confidence, and the Lord thrice answered him that he would deny Him thrice before cock-crowing; as after His resurrection He thrice asked him if he loved Him, and as often gave him command to feed His sheep. …

Catena Aurea by Aquinas ↗

Jerome

Jesus said to him: Truly I say to you, that in this night before the rooster crows, you will deny me three times. And Peter, with fervor of faith, promised, and the Savior, as if God, knew the future. And note that Peter will deny in the night, and deny a third time. But after the rooster crowed, and the darkness diminishing, the approaching light was announced, he turned and wept bitterly, washing away the stains of denial with tears of repentance.

Commentary on Matthew ↗

Thomas Aquinas

Jesus said to him: amen I say to thee, that in this night before the cock crow, thou wilt deny me thrice. Because you might think that I speak by way of threat, therefore I say to you, amen, i.e., from the heart I say to you, that before the cock crow in this night, thou wilt deny me thrice. And his fault is aggravated by the nearness of time, because in this night. …

Commentary on Matthew ↗