Sahih Bukhari
Manumission of Slaves
Volume: 003 / Book Number: 046 / Hadith Number: 724
Narrated Abu Huraira:
Allah's Apostle 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.