Sahih Muslim Book 10, Hadith Number 3745.

Rafi (Allah be pleased with him) reported that Zuhair b. Rafi (who was his uncle) came to me and said: Allah’s Messenger (may peace be upon him) forbade a practice which was useful for us. I said: What is this? (I believe) that whatever Allah’s Messenger (may peace be upon him) says is absolutely true. He (Zuhair) said that he (the Holy Prophet) asked me: What do you do with your cultivable lands? I said: Allah’s Messenger, we rent those irrigated by canals for dry dates or barley. He said: Don’t do that. Cultivate them or let them be cultivated (by others) or retain them yourself.