Sahih Bukhari
Sales in which a Price is paid for Goods to be Delivered Later (As-Salam)
Volume: 003 / Book Number: 035 / Hadith Number: 448
Narrated Muhammad bin Abi Al-Mujalid:
as above (446) and said, "We used to pay them in advance for wheat and barley (to be delivered later). Narrated Ash-Shaibani--"And also for oil."