Bukhari Collection: ::Book Number 8:: Hadith # 37
Narrated Abu Sulaiman and Malik bin Huwairith:We came to the Prophet and we were (a few) young men of approximately equal age and stayed with him for twenty nights. Then he thought that we were anxious for our families, and he asked us whom we had left behind to look after our families, and we told him. He was kindhearted and merciful, so he said, "Return to your families and teach them (religious knowledge) and order them (to do good deeds) and offer your prayers in the way you saw me offering my prayers, and when the stated time for the prayer becomes due, then one of you should pronounce its call (i.e. the Adhan), and the eldest of you should lead you in prayer.