Sahih Bukhari Volume 4, Book 56, Hadith Number 798.

Narated By Sasaa : Abu Said Al-Khudr said to me, “I notice that you like sheep and you keep them; so take care of them and their food, for I have heard Allah’s Apostle saying, ‘A time will come upon the people when the best of a Muslim’s property will be sheep, which he will take to the tops of mountains and to the places of rain-falls to run away with his religion in order to save it from afflictions.'”