[Machine] I used to sell camels in al-Baqi' and people would bring me dirhams and I would sell them to a man for dinars, and he would give them to me tomorrow. So, I went to the Messenger of Allah ﷺ and asked him about this. He said, "If you sell something to a man for gold or silver, do not separate from him until the transaction is completed, and there is some kind of clothing between you." It is narrated in one of the two narrations from Isra'il from Simak and from Abu Al-Ahwas from Simak, and the hadith is unique in its elevation of Simak bin Harb [as the transmitter] from Sa'id bin Jubair among the companions of Ibn 'Umar.  

كُنْتُ أَبِيعُ الْإِبِلَ بِالْبَقِيعِ فَيَجْتَمِعُ عِنْدِي مِنَ الدَّرَاهِمِ فَأَبِيعُهَا مِنَ الرَّجُلِ بِالدَّنَانِيرِ وَيُعْطِينِيهَا لِلْغَدِ فَأَتَيْتُ رَسُولَ اللهِ ﷺ فَسَأَلْتُهُ عَنْ ذَلِكَ فَقَالَ إِذَا بَايَعْتَ الرَّجُلَ بِالذَّهَبِ وَالْفِضَّةِ فَلَا تُفَارِقْهُ وَبَيْنَكُمَا لُبْسٌ وَبِقَرِيبٍ مِنْ مَعْنَاهُ رُوِيَ فِي إِحْدَى الرِّوَايَتَيْنِ عَنْ إِسْرَائِيلَ عَنْ سِمَاكٍ وَعَنْ أَبِي الْأَحْوَصِ عَنْ سِمَاكٍ وَالْحَدِيثُ يَنْفَرِدُ بِرَفْعِهِ سِمَاكُ بْنُ حَرْبٍ عَنْ سَعِيدِ بْنِ جُبَيْرٍ مِنْ بَيْنِ أَصْحَابِ ابْنِ عُمَرَ