It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that I used to sell camels in Jannat al-Baqi'. If I sold for dinars, I would take dirhams from the buyer, and if I sold for dirhams, I would take dinars from him. One day, I came to the Prophet (peace and blessings be upon him) to ask about this issue. At that time, he (peace and blessings be upon him) was entering his chamber. I held onto his garment and asked him about this issue. He (peace and blessings be upon him) said: "When you receive one of the two (currencies) in exchange for the other, do not separate from your companion until there remains no transaction between you and him."