Sahih Muslim 1602
Sahih Muslim · Book 22: The Book of Musaqah · The permissibility of selling animals for animals of the same kind and of different quality
Jabir (Allah be pleased with him) reported:
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ ، وَابْنُ، رُمْحٍ قَالاَ أَخْبَرَنَا اللَّيْثُ ، ح وَحَدَّثَنِيهِ قُتَيْبَةُ، بْنُ سَعِيدٍ حَدَّثَنَا لَيْثٌ ، عَنْ أَبِي الزُّبَيْرِ ، عَنْ جَابِرٍ ، قَالَ جَاءَ عَبْدٌ فَبَايَعَ النَّبِيَّ صلى الله عليه وسلم عَلَى الْهِجْرَةِ وَلَمْ يَشْعُرْ أَنَّهُ عَبْدٌ فَجَاءَ سَيِّدُهُ يُرِيدُهُ فَقَالَ لَهُ النَّبِيُّ صلى الله عليه وسلم " بِعْنِيهِ " . فَاشْتَرَاهُ بِعَبْدَيْنِ أَسْوَدَيْنِ ثُمَّ لَمْ يُبَايِعْ أَحَدًا بَعْدُ حَتَّى يَسْأَلَهُ " أَعَبْدٌ هُوَ " .
There came a slave and pledg- ed allegiance to Allah's Apostle (ﷺ) on migration; he (the Holy Prophet) did not know that he was a slave. Then there came his master and demanded him back, whereupon Allah's Apostle (ﷺ) said: Sell him to me. And he bought him for two black slaves, and he did not afterwards take allegiance from anyone until he had asked him whether he was a slave (or a free man)