not his property, nor does he have permission to sell it, also to validate the contract. It is possible to validate the contract here by setting the genus in exchange for the other genus, or by setting the non-genus in exchange for the surplus over the equivalent. Our evidence is what Fadala ibn 'Ubayd reported, saying: The Prophet (peace and blessings of Allah be upon him) was brought a necklace containing gold and beads, and a man bought it for nine dinars or seven dinars. The Prophet (peace and blessings of Allah be upon him) said: "No, until you separate between them." He said: So he returned it until he separated between them. This was narrated by Abu Dawud. In a version narrated by Muslim, he said: The Messenger of Allah (peace and blessings of Allah be upon him) ordered the gold in the necklace to be removed on its own, then the Messenger of Allah (peace and blessings of Allah be upon him) said to them: "Gold for gold, weight for weight." This is because when a contract brings together two items of different genera, it is necessary that one of them be distributed over the other according to the value of the other in itself. Thus, if the values differ, the amount received in compensation differs. The explanation for this is that if he buys two slaves, where the value of one is equal to half the value of the other for ten [dirhams], the price of one is two-thirds of the ten, and the other is one-third. If he returned one of them due to a defect, he would return it for its proportionate share of the price. Likewise, if he bought a share of property and a sword for a price, the pre-emptor takes the share of property for its proportionate share of the price. Therefore, if we do this for one who sells a dirham and a mudd, the value of which is two dirhams, for two mudds, the value of which is three [dirhams], the dirham corresponds to two-thirds of a mudd, and the mudd that is with the dirham corresponds to a mudd and one-third. This applies when values differ; when they are equal, it remains unknown, because valuation is [a matter of] conjecture and estimation, and ignorance of equality is like knowledge of its absence in the realm of usury (riba). For this reason, it is not permissible to sell a heap for a heap by conjecture and estimation. Their argument that "it is necessary to validate the contract" is not so; rather, it should be interpreted.