Hazrat Abu Sa'id Khudri (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: Do not sell gold for gold unless it is equal on both sides; do not allow any decrease or increase on either side. And do not sell silver for silver unless it is equal on both sides; do not allow any decrease or increase on either side. And do not sell deferred payment for immediate payment.