From Sahih Bukhari (Hadith 1467):
Narrated Zainab:(the daughter of Um Salama) My mother said, "O Allah's Messenger (ﷺ)! 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 (ﷺ) replied, "Spend on them and you will get a reward for what you spend on them
Reference: Bukhari 1467