Sahih Bukhari
Sales and Trade
Volume: 003 / Book Number: 034 / Hadith Number: 342
Narrated Tawus:
Ibn 'Abbas said, "Allah's Apostle forbade the selling of foodstuff before its measuring and transferring into one's possession." I asked Ibn 'Abbas, "How is that?" Ibn 'Abbas replied, "It will be just like selling money for money, as the foodstuff has not been handed over to the first purchaser who is the present seller."