Hadith 9:50
Sahih (Al-Albani)
Abu Burda reported from his father that the Messenger of Allah, may Allah bless him and grant him peace, said, "The slave has two rewards when he carries out Allah's due in worship (or he said that he is excellent in his worship) and the right of his owner who owns him."
حَدَّثَنَا مُوسَى، قَالَ: حَدَّثَنَا عَبْدُ الْوَاحِدِ، قَالَ: حَدَّثَنَا أَبُو بُرْدَةَ بْنُ عَبْدِ اللهِ بْنِ أَبِي بُرْدَةَ قَالَ: سَمِعْتُ أَبَا بُرْدَةَ يُحَدِّثُ، عَنْ أَبِيهِ قَالَ: قَالَ رَسُولُ اللهِ صلى الله عليه وسلم: الْمَمْلُوكُ لَهُ أَجْرَانِ إِذَا أَدَّى حَقَّ اللهِ فِي عِبَادَتِهِ، أَوْ قَالَ: فِي حُسْنِ عِبَادَتِهِ، وَحَقَّ مَلِيكِهِ الَّذِي يَمْلِكُهُ
Original Reference: Al-Adab Al-Mufrad 205