Sahih Bukhari Volume 003, Book 039, Hadith Number 523.
Narated By 'Amr : I said to Tawus, "I wish you would give up Mukhabara (Share-cropping), for the people say that the Prophet forbade it." On that Tawus replied, "O 'Amr! I give the land to share-croppers and help them. No doubt; the most learned man, namely Ibn 'Abbas told me that the Prophet had not forbidden it but said, 'It is more beneficial for one to give his land free to one's brother than to charge him a fixed rental."