Numbers 22:28
And the LORD opened the mouth of the ass, and she said unto Balaam, What have I done unto thee, that thou hast smitten me these three times? And the LORD opened the mouth of the ass, and she said unto Balaam, What have I done unto thee, that thou hast smitten me these three times?
The donkey turned aside from the road because it saw the angel of the Lord standing in the way to block its path, while Balaam himself did not see him. The angel had been sent because the Lord's anger was kindled against Balaam for going to Balak on his way to curse Israel, acting against the Lord's will in presumptuous folly. He stood ready to kill and destroy Balaam for that course. God opened the donkey's mouth to speak in a human voice, asking why Balaam had beaten her three times and protesting being struck.
Balaam noticed nothing remarkable in the donkey speaking, because he was blinded by passion and anger and beside himself with rage. Her speech exposed his cruel treatment and interrupted his journey, and God used the animal to rebuke the prophet's madness. The angel stood as a witness against Balaam's cruelty and abuse and spoke on behalf of the speechless animal that could not protest for itself, showing that God sees and opposes cruelty to animals and holds people accountable for it.
When the angel revealed himself, Balaam was terrified and bowed in humility before him. The angel told him he had come to oppose him because his way was perverse, warned him strongly against gratifying the Moabites, yet permitted him to continue his journey. Permission to continue was given so God would glorify His name even through presumptuous Balaam before the enemies of Israel, by showing that a man of covetous disposition dared not pronounce a curse against Israel for any promises of promotion or rewards. Balaam worked contrary to God because he brought selfishness and covetousness into his work and left God out of his heart and plans. In the wider account, Balak led Balaam from one place to another in repeated, vain efforts to turn Israel's blessing into a curse, but the blessing could not be turned into a curse, and neither human applause nor fear of man could shake one sustained by divine power from steadfast resolve. The episode shows that God can intervene to restrain those set on doing evil.