The Prophet (ﷺ) came (to Medina) and he told the people (regarding the payment of money in advance that they should pay it) for a known specified measure and a known specified weight and a known specified period.
Sahih al-Bukhari Book 35, Hadith 5
← Previous Hadith as above, saying, "He should pay the price in advance for a specified measure and for a specified period."

Sahih al-Bukhari Book 35, Hadith 4 Next Hadith → Muhammad or `Abdullah bin Abu Al-Mujalid said, "Abdullah bin Shaddad and Abu Burda differed regarding As-Salam, so they sent me to Ibn Abi `Aufa and I asked him about it. He replied, 'In the lifetime of Allah's Messenger (ﷺ), Abu Bakr and `Umar, we used to pay in advance the prices of wheat, barley, dried grapes and dates to be delivered later. I also asked Ibn Abza and he, too, replied as above.' "

Sahih al-Bukhari Book 35, Hadith 6