As the Israelites passed through the land of Moab, the king of Moab sent for a pagan prophet named Balaam to bring a curse against the Israelites.  When Balaam was riding his donkey up a narrow path, the donkey stopped.  Balaam tried numerous beatings and threats, but the donkey would not move forward.  Finally, God allowed Balaam to see what his donkey had seen all along: there was an angel in the path.  The angel commanded Balaam not to curse Israel, but only to speak the words God told him to say.