Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) came to Madinah while the people of Madinah were making advance sales in fruits for two and three years. The Messenger of Allah (peace and blessings be upon him) said: "Make advance sales in fruits on condition of a known measure and a known term." In one narration it is: "Make advance sales in fruits on condition of a known measure, a known weight and a known term."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11090
Muhammad, or Abdullah, bin Abi al-Mujalid (may Allah have mercy on him) said: Abdullah bin Shaddad and Abu Burdah differed about the advance sale (salaf), so they sent me to Ibn Abi Awfa (may Allah be pleased with him). I asked him, and he replied: We used to make advance sales in the time of the Messenger of Allah (peace and blessings be upon him), Abu Bakr and Umar (may Allah be pleased with them both) in wheat, barley, dates and raisins. Ibn Kathir added: we used to make this sale with people who did not have these things. Then the two narrations continue alike: I then asked Ibn Abza (may Allah be pleased with him) about the same matter, and he too gave the same answer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11091
Muhammad bin Abi al-Mujalid (may Allah have mercy on him) says: Abdullah bin Shaddad (may Allah have mercy on him) and Abu Burdah (may Allah have mercy on him) sent me to Ibn Abza and Ibn Abi Awfa (may Allah be pleased with them both). I asked the two of them about the salaf sale (advance payment), and they replied: "With the Messenger of Allah (peace and blessings be upon him) we used to receive a share of the spoils of war. Then the people of Syria would come to us, and we would make salaf contracts with them for wheat, barley and olive oil to a fixed term." It was said to them: "Did they have crops?" They replied: "We did not ask them about that."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11092
Abu Mu'awiyah from Yahya bin Sa'id, and Ibrahim bin Muhammad from Yahya bin Sa'id, from Nafi', from Sayyiduna Ibn Umar (may Allah be pleased with them both): that he saw no harm in a man selling something of his to a known term while he did not have its source (the actual goods) with him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11093