Sunan An-Nasai, Chapter: The Book of the Adhan (The Call to Prayer)

that he was with the Messenger of Allah (saw) on a journey, and he hear the voice of a man calling the Adhan, and he said what he said. When he reached the words: Ashhadu anna Muhammad (SAW)an Rasulullah (I bear witness that Muhammad (SAW) is the Messenger of Allah), - Al-Hakam said, "I did not hear this from Ibn Abi Lailah" - the Messenger of Allah (saw) said: "This is a shepherd or a man who is away from his family." He went down into the valley and found a shepherd, standing by a dead sheep. He said: "Do you think that this is worthless to its owners?" They said: "Yes." He said: "This world is more worthless to Allah than this (dead sheep) is to its owners." (Hasan)