Theophylact of Ohrid

Now consider how many things the Lord foretold to His disciples, that they should find a colt; wherefore it goes on, And as soon as ye be entered into it, ye shall find a colt tied, whereon never man sat, loose him, and bring him; and that they should be impeded in taking it, wherefore there follows, And if any man say unto you, Why do ye this? …

Catena Aurea by Aquinas ↗

Justin Martyr

And we will cite the prophetic utterances of another prophet, Zephaniah, to the effect that He was foretold expressly as to sit upon the foal of an ass and to enter Jerusalem. The words are these: "Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee; lowly, and riding upon an ass, and upon a colt the foal of an ass."

The First Apology, Chapter XXXV ↗

Bede

And immediately upon entering it, you will find a colt tied, upon which no man has yet sat. Untie it and bring it. And if anyone says to you: What are you doing? say: Because the Lord needs it, and immediately he will send it here. Entering the world, the holy preachers found the people of the nations ensnared by the bonds of perfidy. For each was bound by the cords of their sins; not only of the nations, but also of the Jews. For all have sinned and fall short of the glory of God (Rom. III). …

On the Gospel of Mark ↗