Augustine of Hippo

"Let his days be few" [Psalm 109:7]. By "his days," he meant the days of his apostleship, which were few; since before the Passion of our Lord, they were ended by his crime and death. And as if it were asked, What then shall become of that most sacred number twelve, within which our Lord willed, not without a meaning, to limit His twelve first Apostles? He at once adds, "and let another take his office." As much as to say, let both himself be punished according to his desert, and let his number be filled up.

Exposition on Psalm 109 ↗

Jerome

When he is judged, let him come forth condemned. Let him come not into judgment, but into condemnation. For where there is judgment, there is doubt: but where there is condemnation, the sentence is already plain. And let his prayer be turned into sin. The repentance of Judas was made a worse sin. How was the repentance of Judas made a worse sin? He went and perished by hanging; and he who became the betrayer of the Lord, this same man came to be his own slayer. …

Homily 35, on Psalm 108 ↗

Gregory the Dialogist

But still, what is more serious, another asks for the death of an enemy, and the one whom he cannot pursue with a sword, he pursues with prayer. And the one who is cursed still lives, yet the one who curses is already held guilty of his death. But God commands that an enemy be loved, and yet God is asked to kill an enemy. Whoever therefore prays in this way fights against the Creator in his very prayers. …

Forty Gospel Homilies, Homily 27 ↗