Sahih Bukhari
Sales and Trade
Volume: 003 / Book Number: 034 / Hadith Number: 419
Narrated 'Abdur-Rahman bin Abu Bakr:
We were with the Prophet when a tall pagan with long matted unkempt hair came driving his sheep. The Prophet asked him, "Are those sheep for sale or for gifts?" The pagan replied, "They are for sale." The Prophet bought one sheep from him.