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

Bukhari :: Book 4 :: Volume 53 :: Hadith 392

Narrated Abu Huraira:

While we were in the Mosque, the Prophet came out and said, "Let us go to the Jews" We went out till we reached Bait-ul-Midras. He said to them, "If you embrace Islam, you will be safe. You should know that the earth belongs to Allah and His Apostle, and I want to expel you from this land. So, if anyone amongst you owns some property, he is permitted to sell it, otherwise you should know that the Earth belongs to Allah and His Apostle."