Sahih Bukhari Volume 007, Book 065, Hadith Number 364.
Narrated By Jabir bin 'Abdullah : We were with Allah's Apostle collecting Al-Kabath at Mar-Az-Zahran. The Prophet said, "Collect the black ones, for they are better." Somebody said, (O Allah's Apostle!) Have you ever shepherded sheep?" He said, "There has been no prophet but has shepherded them."