Sahih Bukhari Volume 003, Book 039, Hadith Number 525.
Narated By Rafi : We worked on farms more than anybody else in Medina. We used to rent the land and say to the owner, "The yield of this portion is for us and the yield of that portion is for you (as the rent)." One of those portions might yield something and the other might not. So, the Prophet forbade us to do so.