Sahih Al Bukhari Hadith Number 1467

Narrated Zainab: (the daughter of Um Salama) My mother said, “O Allah’s Messenger (peace be upon him)! 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 (peace be upon him) replied, “Spend on them and you will get a reward for what you spend on them.”