From Sahih Bukhari (Hadith 3939):
Narrated Abu Al-Minhal `AbdurRahman bin Mut`im:A partner of mine sold some Dirhams on credit in the market. I said, "Glorified be Allah! Is this legal?" He replied, "Glorified be Allah! By Allah, when I sold them in the market, nobody objected to it." Then I asked Al-Bara' bin `Azib (about it) he said, "We used to make such a transaction when the Prophet came to Medina. So he said, 'There is no harm in it if it is done from hand to hand, but it is not allowed on credit.' Go to Zaid bin Al- Arqam and ask him about it for he was the greatest trader of all of us." So I asked Zaid bin Al-Arqam., and he said the same (as Al-Bara) did
Reference: Bukhari 3939