Numbers 22:20-23

²⁰And word came from before the Lord unto Bileam by night, and said to him: If the men come to call thee, arise and go with them; nevertheless the word that I speak with thee, that thou shalt do.

²¹And Bileam rose up in the morning, and saddled his ass, and went with the princes of Moab.

²²But the displeasure of the Lord was provoked because he (so) went; and the angel of the Lord stood in the road to withstand him: and he was riding upon his ass, and his two young men with him.

²³And the ass discerned the angel of the Lord standing in the way with his sword drawn in his hand; and the ass started aside from the road, and went into the field. And Bileam struck the ass to make her to return into the road.