Fighting for the Cause of Allah (Jihaad)

Bukhari :: Book 4 :: Volume 52 :: Hadith 193

Narrated Anas:

Whenever Allah's Apostle attacked some people, he would never attack them till it was dawn. If he heard the Adhan (i.e. call for prayer) he would delay the fight, and if he did not hear the Adhan, he would attack them immediately after dawn. We reached Khaibar at night.