It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that once he asked the Prophet (peace and blessings be upon him): "Can I buy gold in exchange for silver?" The Noble Prophet (peace and blessings be upon him) said: "Whenever you take either of these two things, do not separate from your companion until there is not even the slightest doubt between you and him."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4883
Hadith Gradingحکم دارالسلام:إسناده ضعيف لانفراد سماك بن حرب برفعه، قال النسائي: إذا انفرد بأصل لم يكن حجة، لأنه كان ربما يلقن فيتلقن