Sahih Bukhari
Beginning of Creation
Volume: 004 / Book Number: 054 / Hadith Number: 519
Narrated Abu Said al-Khudri:
Allah's Apostle said, "There will come a time when the best property of a man will be sheep which he will graze on the tops of mountains and the places where rain falls (i.e. pastures) escaping to protect his religion from afflictions."