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

Bukhari :: Book 4 :: Volume 53 :: Hadith 328

Narrated Abu Huraira:

Allah's Apostle said, "My heirs should not take even a single Dinar (i.e. anything from my property), and whatever I leave, excluding the expenditure of my wives and my laborers, will be Sadaqa (i.e. be used for charity)."'