Jesus found a young donkey and sat upon it, as it is written,

“found” = through the disciples (Mr 11:2 -6; Mt 21:2 -3,6; Lu 19:30). John is not interested in these details; they have nothing to do with his purpose in writing his account.

Mark 11:2-6  saying to them, “Go to the village ahead of you, and just as you enter it, you will find a colt tied there, which no-one has ever ridden. Untie it and bring it here.  If anyone asks you, ‘Why are you doing this?’ tell him, ‘The Lord needs it and will send it back here shortly.’”  They went and found a colt outside in the street, tied at a doorway. As they untied it,  some people standing there asked, “What are you doing, untying that colt?”  They answered as Jesus had told them to, and the people let them go.

Matthew 21:2-3  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, tell him that the Lord needs them, and he will send them right away.”

Matthew 21:6  The disciples went and did as Jesus had instructed them.

Luke 19:30  “Go to the village ahead of you, and as you enter it, you will find a colt tied there, which no-one has ever ridden. Untie it and bring it here.

The colt has never been ridden by men (Mark 11:2). If it had, it would have been unfit for sacred purposes (Num 19:2, Deut 21:3, 1 Sam 6:7).

Mark 11:2  saying to them, “Go to the village ahead of you, and just as you enter it, you will find a colt tied there, which no-one has ever ridden. Untie it and bring it here.

Numbers 19:2  “This is a requirement of the law that the LORD has commanded: Tell the Israelites to bring you a red heifer without defect or blemish and that has never been under a yoke.

Deuteronomy 21:3  Then the elders of the town nearest the body shall take a heifer that has never been worked and has never worn a yoke

1 Samuel 6:7  “Now then, get a new cart ready, with two cows that have calved and have never been yoked. Hitch the cows to the cart, but take their calves away and pen them up.