From Sahih Bukhari (Hadith 2548):
Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "A pious slave gets a double reward." Abu Huraira added: By Him in Whose Hands my soul is but for Jihad (i.e. holy battles), Hajj, and my duty to serve my mother, I would have loved to die as a slave
Reference: Bukhari 2548