Sahih Bukhari
Obligatory Charity Tax (Zakat)
Volume: 002 / Book Number: 024 / Hadith Number: 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."