Mishkat al-Masabih #613

Anas said that the Prophet used to attack the enemy at dawn, and he would sometimes hear the adhan, so if he heard an adhan he stopped, but otherwise he attacked. Once on hearing a man say, “God is most great, God is most great,” God’s Messenger said, “You follow Islam.” Then hearing him say, “There is no god but God,” he said, “You have come forth from hell.” They looked at him and found that he was a goatherd. Muslim transmitted it.