Sahih Bukhari Volume 002, Book 024, Hadith Number 546.

Narated By 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."

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