1362/1 - Ibn ‘Umar (may Allah be pleased with him and his father) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “If a slave serves his master sincerely and worships Allah properly, he will have a double reward.” [Narrated by Al-Bukhāri and Muslim]
1363/2 - Abu Hurayrah (may Allah be pleased with him) reported: “The Prophet (may Allah’s peace and blessings be upon him) said: ‘The sincere slave will receive a double reward.’ By the One in Whose hand the soul of Abu Hurayrah is, were it not for Jihad in the cause of Allah, Hajj, and dutifulness to my mother, I would have liked to die as a slave.” [Narrated by Al-Bukhāri and Muslim]
1364/3 - Abu Mūsa al-Ash‘ari (may Allah be pleased with him) reported: The Messenger of Allah (may Allah’s peace and blessings be upon him) said: “A slave who worships his Lord properly and fulfills the due right of his master, being sincere and obedient to him, will have a double reward.” [Narrated by Al-Bukhāri]
1) If a slave worships Allah properly and serves his master sincerely, he will receive a double reward. This is an honor that the Shariah bestows on the slave and an elevation of the rank of his servitude to Allah Almighty so that his reward would be greater.
2) A slave is trusted with his master’s property and is responsible for it. So, everyone should fear Allah with regard to his responsibilities.
Imām Al-Hāfizh Ibn ‘Abd al-Barr (may Allah have mercy upon him) said: “In my view, this Hadīth indicates the following: Since a slave is required to perform two obligations - to obey and worship his Lord and obey his master in what is good - and he actually fulfills them, he obtains a reward like a free man who obeys Allah Almighty, in addition to that, he gets a reward for obeying his master, whom Allah has commanded him to obey.”
Al-Hāfizh Ibn Hajar said: “The great merit that the slave deserves is apparently due to the hardship associated with slavery.” [Fat'h al-Bāri Sharh Sahīh al-Bukhāri]
1365/3 - He also reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “Three types of people will receive a double reward: a man from the people of the Book who believed in his prophet and then believed in Muhammad; a slave who fulfilled his duties towards Allah and towards his masters; and a man who had a female slave and he taught her good manners, educated her well, and then freed her and married her; he will receive a double reward.” [Narrated by Al-Bukhāri and Muslim]
1) It shows the generosity of Islam as it doubles the reward for those who properly perform two obligations required of them under the Shariah.
2) A prudent man would teach and educate his family and treat them kindly, as the free women are more deserving of attention than the female slaves.
Commenting on the preceding Hadīth, the erudite scholar Al-Tāhir ibn ‘Āshūr (may Allah have mercy upon him) said:
“In my opinion, one of the reasons behind this is that when a slave of this kind remains in bondage, this will deprive society of benefiting from him in a full manner. So, it is more beneficial for society to admit him into the category of free people.” [The Objectives of Islamic Law]