Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: When the Prophet Muhammad (peace and blessings be upon him) arrived in Madinah, the people there used to conduct salam (advance sale) transactions in dates for two or three years. The Prophet Muhammad (peace and blessings be upon him) said:“Whoever wants to do a salam transaction should do so for a specified quantity of dates, with a specified weight or a specified measure, for a specified period.”