Musannaf Ibn Abi Shaybah 23748 — Paying in advance (salam) for food

Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: When the Prophet (peace and blessings be upon him) came to Madinah, the people used to make salam transactions in dates for one, two, and three years. The Prophet (peace and blessings be upon him) said: "Whoever makes a salam sale in dates should do so with a known measure and weight, and for an appointed time."