Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them) that the Messenger of Allah (peace and blessings be upon him) said: "When a slave becomes sincere to his master and worships his Lord in a good manner, he will receive a double reward."

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him), the Messenger of Allah (peace and blessings be upon him) said: "A righteous slave has two rewards." (Then Sayyiduna Abu Hurairah, may Allah be pleased with him, said) By Him in Whose hand is the life of Abu Hurairah! If it were not for matters such as striving in the way of Allah, Hajj, and being good to my mother, I would have preferred to die the death of a slave.

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When a slave is sincere to his master and worships Allah Almighty in a good manner, then for him there is a double reward."