Obligatory Charity Tax (Zakat)

Bukhari :: Book 2 :: Volume 24 :: Hadith 571

Narrated Um 'Atiyya Al-Ansariya :

The Prophet went to 'Aisha and asked her whether she had something (to eat). She replied that she had nothing except the mutton (piece) which Nusaiba (Um 'Atiyya) had sent to us (Buraira) in charity." The Prophet said, "It has reached its place and now it is not a thing of charity but a gift for us."