Yahya related to me from Malik that he had heard that al-Oasimibn Muhammad said, ''Umar ibn al-Khattab said, 'A dinar for a dinar,and a dirham for adirham, and a sa for a sa. Something to be collectedlater is not to be sold for something at hand. ' " (DE)
USC-MSA web (English) reference: Book 31, Hadith 36 (DE)
Arabic reference (DE): Book 31, Hadith 1327 (DE)