Sahih Bukhari
One-fifth of Booty to the Cause of Allah (Khumus)
Volume: 004 / Book Number: 053 / Hadith Number: 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)."'