Sahih Muslim Book 10, Hadith Number 3859.

Chapter : Accepting that which is lawful and abandoning that which is doubtful.

Abu Minhal reported: My partner sold silver to be paid in the (Hajj) season or (in the days of) Hajj. He (my partner) came to me and informed me, and I said to him: Such transaction is not desirable. He said: I sold it in the market (on loan) but nobody objected to this. I went to al-Bara’ b. ‘Azib and asked him, and he said: Allah’s Apostle (may peace be upon him) came to Medina and we made such transaction, whereupon he said: In case the payment is made on the spot, there is no harm in it, and in case (it is ‘sold) on loan, it is usury. You better go to Zaid b. Arqam, for he is a greater trader than I; so I went to him and asked him, and he said like it.