It is narrated from Hazrat Abu Saeed Khudri (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Sell gold for gold and silver for silver in equal measure; do not increase or decrease in it." And he said: "When the heat becomes intense, perform the prayer at a cooler time, for the intensity of heat is from the effect of the heat of Hell."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 11062