Obligatory Charity Tax (Zakat)

Bukhari :: Book 2 :: Volume 24 :: Hadith 546

Narrated Zainab,:

(the daughter of Um Salama) My mother said, "O Allah's Apostle! Shall I receive a reward if I spend for the sustenance of Abu Salama's offspring, and in fact they are also my sons?" The Prophet replied, "Spend on them and you will get a reward for what you spend on them."