Sunan an-Nasai 19329
In-book no 4593أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ سِمَاكٍ، عَنِ ابْنِ جُبَيْرٍ، عَنِ ابْنِ عُمَرَ، قَالَ كُنْتُ أَبِيعُ الذَّهَبَ بِالْفِضَّةِ أَوِ الْفِضَّةَ بِالذَّهَبِ فَأَتَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَخْبَرْتُهُ بِذَلِكَ فَقَالَ " إِذَا بَايَعْتَ صَاحِبَكَ فَلاَ تُفَارِقْهُ وَبَيْنَكَ وَبَيْنَهُ لَبْسٌ " .
It was narrated that Ibn 'Umar said: "I used to sell gold for silver, or silver for gold. I came to the Messenger of Allah and told him about that, and he said: 'If you make a deal with your companion, d o not leave him when there is still any ambiguity (in the deal) between you."'