It was narrated that Jabir Sair:

"A slave came and gave his pledge to the Messenger of Allah to emigrate, and the Prophet did not realize that he was a slave. Then his master came looking for him. The Prophet ﷺ said; 'Sell him to me.' So he bought him for two black slaves, then he did not accept until he had asked; 'Is he a slave?'''

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ جَاءَ عَبْدٌ فَبَايَعَ رَسُولَ اللَّهِ ﷺ عَلَى الْهِجْرَةِ وَلاَ يَشْعُرُ النَّبِيُّ ﷺ أَنَّهُ عَبْدٌ فَجَاءَ سَيِّدُهُ يُرِيدُهُ فَقَالَ النَّبِيُّ ﷺ " بِعْنِيهِ " . فَاشْتَرَاهُ بِعَبْدَيْنِ أَسْوَدَيْنِ ثُمَّ لَمْ يُبَايِعْ أَحَدًا بَعْدُ حَتَّى يَسْأَلَهُ أَعَبْدٌ هُوَ