I used to buy dates from one of the Jewish clans who were called Banu Qainuqaʿ, and sell them at a profit. News of that reached the Messenger of Allah ﷺ who said: ʿO ʿUthman, when you buy, take your dues with nothing extra, and when you sell, give (the other partyʿs) dues with nothing less.ʿ Moosa bin Wardan narrated from Saʿeed bin al-Musayyab from ‘Uthman bin ʿAffan ؓ ... and he mentioned a similar report.  

يَقُولُ سَمِعْتُ عُثْمَانَ يَخْطُبُ عَلَى الْمِنْبَرِ وَهُوَ يَقُولُ كُنْتُ أَبْتَاعُ التَّمْرَ مِنْ بَطْنٍ مِنَ الْيَهُودِ يُقَالُ لَهُمْ بَنُو قَيْنُقَاعَ فَأَبِيعُهُ بِرِبْحٍ فَبَلَغَ ذَلِكَ رَسُولَ اللهِ ﷺ فَقَالَ يَا عُثْمَانُ إِذَا اشْتَرَيْتَ فَاكْتَلْ وَإِذَا بِعْتَ فَكِلْ  

I heard ‘Uthman ؓ delivering a khutbah from the minbar. He said: I used to buy dates from one of the Jewish clans who were called Banu Qainuqaʿ, and sell them at a profit. News of that reached the Messenger of Allah ﷺ who said: ʿO ʿUthman, when you buy, take your dues with nothing extra, and when you sell, give (the other partyʿs) dues with nothing less.ʿ  

يَقُولُ سَمِعْتُ عُثْمَانَ يَخْطُبُ عَلَى الْمِنْبَرِ وَهُوَ يَقُولُ كُنْتُ أَبْتَاعُ التَّمْرَ مِنْ بَطْنٍ مِنَ الْيَهُودِ يُقَالُ لَهُمْ بَنُو قَيْنُقَاعٍ فَأَبِيعُهُ بِرِبْحِ الْآصُعِ فَبَلَغَ ذَلِكَ النَّبِيَّ ﷺ فَقَالَ يَا عُثْمَانُ إِذَا اشْتَرَيْتَ فَاكْتَلْ وَإِذَا بِعْتَ فَكِلْ