Muhammad bin Abi al-Mujalid (may Allah have mercy on him) says: Abu Burdah and Abdullah bin Shaddad (may Allah have mercy on them both) sent me to Ibn Abi Awfa (may Allah be pleased with him) to go and ask: "Did you make salaf sales in the time of the Messenger of Allah (peace and blessings be upon him) in wheat, barley and raisins?" I went and asked, and he replied: "We used to make salam sales with the Nabataeans of Syria in barley, wheat and raisins, for a known measure, to a fixed term." I asked: "Did you deal with those who had crops?" He said: "We did not ask them about that." Muhammad bin Abi al-Mujalid (may Allah have mercy on him) says: Then the two of them sent me to Abd al-Rahman bin Abza (may Allah be pleased with him) and said: "Ask him: did the Companions make salam sales in wheat, barley and raisins in the time of the Messenger of Allah (peace and blessings be upon him)?" He said: "Yes! They did so when the measure, quantity and term were known, and they did not ask whether you had crops growing or not."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11122
Al-Qasim bin Muhammad asked Ibn Abbas (may Allah be pleased with them both) about the salam sale in coarse cotton cloth, and he said: "When the weight and the term are known, there is no harm."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11123