One-fifth of Booty to the Cause of Allah (Khumus)

Bukhari :: Book 4 :: Volume 53 :: Hadith 380

Narrated Ibn 'Umar:

Umar bin Al-Khattab expelled all the Jews and Christians from the land of Hijaz. Allah's Apostle after conquering Khaibar, thought of expelling the Jews from the land which, after he conquered it belonged to Allah, Allah's Apostle and the Muslims. But the Jews requested Allah's Apostle to leave them there on the condition that they would do the labor and get half of the fruits (the land would yield). Allah's Apostle said, "We shall keep you on these terms as long as we wish." Thus they stayed till the time of 'Umar's Caliphate when he expelled them to Taima and Ariha.