Sahih Bukhari
Sales and Trade
Volume: 003 / Book Number: 034 / Hadith Number: 361
Narrated Abu Huraira:
Allah's Apostle said, "Whoever buys a sheep which has been kept unmilked for a long period, and milks it, can keep it if he is satisfied, and if he is not satisfied, he can return it, but he should pay one Sa of dates for the milk."