The Messenger of Allah (PBUH) used to raid around the dawn. He listens, and if he heard the call to prayer he would hold on, otherwise he would conduct the raid. Narrator said: So one day, he listened and heard a man saying: Allah is greater, Allah is greater. So he said: On the good nature. Then [the voice] said: I bear witness that there is no god but Allah. So, the Prophet (PBUH) said: You [the voice] came out of the Fire.