Sunan Ibn Majah, Volume 4, Book 24, Hadith 2869 (DarusSalam) ⓘ

It was narrated that Jabir said: “A slave came and gave his pledge to the Prophet, pledging to emigrate, and the Prophet did not realize that he was a slave. Then his master came looking for him, and the Prophet said: ‘Sell him to me,’ and he brought him in exchange for two black slaves. Then after that he did not accept the pledge from anyone until he had asked whether he was a slave.”

حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ، أَنْبَأَنَا اللَّيْثُ بْنُ سَعْدٍ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ جَاءَ عَبْدٌ فَبَايَعَ النَّبِيَّ صلى الله عليه وسلم عَلَى الْهِجْرَةِ وَلَمْ يَشْعُرِ النَّبِيُّ صلى الله عليه وسلم أَنَّهُ عَبْدٌ فَجَاءَ سَيِّدُهُ يُرِيدُهُ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ بِعْنِيهِ ‏" ‏ ‏.‏ فَاشْتَرَاهُ بِعَبْدَيْنِ أَسْوَدَيْنِ ثُمَّ لَمْ يُبَايِعْ أَحَدًا بَعْدَ ذَلِكَ حَتَّى يَسْأَلَهُ أَعَبْدٌ هُوَ