"A slave came to give the pledge to the Prophet (ﷺ) for Hijrah, but the Prophet (ﷺ) did not realize that he was a slave. So his master came, and the Prophet (ﷺ) said: 'Sell him to me.' So he purchased him for two black slaves. After this he (ﷺ) would not take the pledge from anyone until he asked him if he was a slave." [He said:] There is something on this topic from Ibn 'Abbas. [Abu 'Eisa said:] The Hadith of Jabir is Hasan Gharib Sahih, we do not know of it except as a narration of Abu Az-Zubair.
حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّهُ قَالَ جَاءَ عَبْدٌ فَبَايَعَ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى الْهِجْرَةِ وَلاَ يَشْعُرُ النَّبِيُّ صلى الله عليه وسلم أَنَّهُ عَبْدٌ فَجَاءَ سَيِّدُهُ فَقَالَ النَّبِيُّ صلى الله عليه وسلم بِعْنِيهِ . فَاشْتَرَاهُ بِعَبْدَيْنِ أَسْوَدَيْنِ وَلَمْ يُبَايِعْ أَحَدًا بَعْدُ حَتَّى يَسْأَلَهُ أَعَبْدٌ هُوَ . قَالَ وَفِي الْبَابِ عَنِ ابْنِ عَبَّاسٍ . قَالَ أَبُو عِيسَى حَدِيثُ جَابِرٍ حَدِيثٌ حَسَنٌ غَرِيبٌ صَحِيحٌ لاَ نَعْرِفُهُ إِلاَّ مِنْ حَدِيثِ أَبِي الزُّبَيْرِ .
Tirmizi
The Book on Military Expeditions • Hadith 1640