The Messenger of Allah ﷺ said, "How excellent it is for one of them to obey his Lord and fulfill the rights of his master," meaning the slave.Kaab said, "Allah and His Messenger have spoken the truth."
حدثنا ابن أبي عمر حدثنا سفيان عن الأعمش عن أبي صالح
أن رسول الله ﷺ قال نعما لأحدهم أن يطيع ربه ويؤدي حق سيده يعني المملوك وقال كعب صدق الله ورسوله
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Bukhari also recorded it in the Book of Emancipation, in the chapter "When a Slave Does Well in Worshipping His Lord and Is Sincere to His Master," hadith no. 2549, and Muslim, hadith no. 1666, from the hadith of Amash, both in abridged and fuller forms. Amash explicitly stated that he heard it directly.It was also narrated by Hammam [mentioned earlier at 1116], Musa, and Ibn Munabbih, from Abu Hurairah, with the same wording (Muslim, hadith no. 1667).There is also a report on this subject from Abu Umar [to come at 1986].