‘Uthman b. ‘Affan reported Allah’s Messenger (Sall Allah-o-alaihe wa sallam) as saying: “Do not sell a dinar for two dinars and one dirham for two dirhams.”
Malik b. Aus b. Al-Hadathan reported: I came saying who was prepared to exchange dirhams (for my gold), whereupon Talha b. ‘Ubaidullah (Allah be pleased with him) (as he was sitting with ‘Umar b. Khattab) said: “Show us your gold and then come to us (at a later time). When our servant would come we would give you your silver (dirhams due to you).” Thereupon ‘Umar b. Khattab (Allah be pleased with him) said: “Not at all.” By Allah, either give him his silver (coins), or return his gold to him, for Allah’s Messenger (Sall Allah-o-alaihe wa sallam) said: Exchange of silver for gold (has an element of) riba in it, except when (it is exchanged) on the spot; and wheat for wheat is riba unless both are handed over on the spot; barley for barely is riba unless both are handed over on the spot; dates for dates is riba unless both are handed over on the spot. 
Abu Qilaba reported: I was in Syria (having) a circle (of friends), in which was Muslim b. Yasar. There came Abu’l-Ash‘ath. He (the narrator said that they (the friends) called him: Abu’l-Ash’ath, Abu’al-Ash’ath, and he sat down. I asked him: “Narrate to our brother the hadith of ‘Ubada b. Samit.” He said: “Yes,” we went out on an expedition, Mu‘awiya being the leader of the people, and we gained a lot of spoils of war. And there was one silver utensil in what we took as spoils. Mu‘awiya ordered a person to sell it for payment to the people (soldiers). The people made haste in getting that. The news of (this state of affairs) reached ‘Ubada b. Samit, and he stood up and said: I heard Allah’s Messenger (Sall Allah-o-alaihe wa sallam) forbidding the sale of gold by gold, and silver by silver, and wheat by wheat, and barley by barley and dates by dates and salt by salt, except like for like and equal for equal. So he who made an addition or who accepted an addition (committed the sin of taking) riba. So the people returned what they had got. This reached Mu’awiya, and he stood up to deliver an address. He said what is the matter with the people that they narrate from the Messenger of Allah (Sall Allah-o-alaihe wa sallam) such traditions which we did not hear though we saw him (the Holy Prophet) and lived in his company? Thereupon ‘Ubada b. Samit stood up and repeated that narration, and then said: We will definitely narrate what we heard from Allah’s Messenger (Sall Allah-o-alaihe wa sallam) though it may be unpleasant to Mu‘awiya (or he said: Even if it is against his will). 1 don’t mind if I do not remain in his troop in the dark night. Hammad said this or something like this.
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 (Sall Allah-o-alaihe wa sallam) 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.
 There has been a difference of opinion among jurists about the item which entail riba al-fad! Some of them felt that it pertained to only six articles which have been expressly stated in the ahadith. They are gold, silver, dates, wheat, salt and barley. But others disagree with it. For example, Abu Hanifa thought that since all these articles can be measured and weighed so kail and wazn were the distinctive features of these articles. On this analogy, he held that riba al-fadl would arise in respect of all those articles which can be measured or weighed. But Shafai‘ considers qualities of eatability (ta‘am) and being money (thamaniyyat) in these articles. So he included all those articles in this category which could be food items or act as money. Malik thought them to be articles of food and those which could be stored. So he drew his analogy on the basis of these two qualities.
Source: Economic Teachings of Prophet Muhammad (peace be upon him): A Select Anthology of Hadith Literature on Economics, Muhammad Akram Khan. Republished with permission.