Riba al-Fadl (Hadith No. 1900)
Hadith no. 1899 (below) is a repeat. Read it here.
Volume 3, Book 34, Number 404 :
Narrated by ‘Aisha (radiallaahu `anhaa)
The Prophet (sallallaahu `alayhi wasallam) bought some foodstuff from a Jew on credit and mortgaged his armor to him.
Volume 3, Book 34, Number 405 :
Narrated by Abu Said Al-Khudri and Abu Huraira (radiallaahu `anhumaa)
Allah’s Apostle (sallallaahu `alayhi wasallam) appointed somebody as a governor of Khaibar. That governor brought to him an excellent kind of dates (from Khaibar). The Prophet (sallallaahu `alayhi wasallam) asked, “Are all the dates of Khaibar like this?” He replied, “By Allah, no, O Allah’s Apostle (sallallaahu `alayhi wasallam)! But we barter one Sa of this (type of dates) for two Sas of dates of ours and two Sas of it for three of ours.” Allah’s Apostle (sallallaahu `alayhi wasallam) said, “Do not do so (as that is a kind of usury) but sell the mixed dates (of inferior quality) for money, and then buy good dates with that money.”
Riba al-Fadl: The riba of exchange surplus. Any commodity-for-commodity exchange transaction (i. e. barter) in which the exchanged commodities are of the same type but of unequal measure, or the delivery of one commodity is postponed.
We’ve already learnt about it in Exchanging Goods, now we know the term for it.
Go through this link for a detailed description and analysis of Riba al-Fadl.