As they approached Jerusalem and came to Bethphage on the Mount of Olives, Jesus sent two disciples, saying to them, "Go to the village ahead of you, and at once you will find a donkey tied there, with her colt by her. Untie them and bring them to me. If anyone says anything to you, say that the Lord needs them, and he will send them right away."

This took place to fulfill what was spoken through the prophet:

"Say to Daughter Zion, 'See, your king comes to you, gentle and riding on a donkey, and on the colt, the foal of a donkey.'"

Matthew, The Bible