Sahih Al Bukhari Hadith Number 2244

Narrated Muhammad bin Al-Mujalid: `Abdullah bin Shaddad and Abu Burda sent me to `Abdullah bin Abi `Aufa and told me to ask `Abdullah whether the people in the lifetime of the Prophet (peace be upon him) used to pay in advance for wheat (to be delivered later). `Abdullah replied, “We used to pay in advance to the peasants of Sham for wheat, barley and olive oil of a known specified measure to be delivered in a specified period.” I asked (him), “Was the price paid (in advance) to those who had the things to be delivered later?” `Abdullah bin `Aufa replied, “We did not use to ask them about that.” Then they sent me to `Abdur Rahman bin Abza and I asked him. He replied, “The companions of the Prophet (peace be upon him) used to practice Salam in the lifetime of the Prophet; and we did not use to ask them whether they had standing crops or not.”