It is mentioned in Ibn Atha’illah As Sakandary’s famous work, the book of Al-Hikam: Abu Hurairah (RA) narrated: While we were in the company of Rasulullah, he (SAW) suddenly said, “There would be a member of Paradise who would be the one performing the solat with you at dawn”. Abu Hurairah hoped therefore that he would be the one whom the Prophet (SAW) referred to as the member of Paradise. When the dawn came, he prayed behind the Prophet (SAW) and still remained in his company even after the congregation.
Suddenly, a black slave with tattered clothing appeared and offered the customary handshake to the Prophet (SAW). And the Prophet (SAW) recited a prayer for him while all those in the presence of the black slave noticed that there was fragrance emitted from his body. The Prophet (SAW) acknowledged that he was a slave from a particular tribe. Abu Hurairah then asked, “Why did you not free him from slavery then, O Messenger of Allah?”