If there is no evidence, or if he has evidence but we say that his evidence is not accepted, and he claims that the purchaser knows of his error, but the purchaser denies it, then the statement is that of the purchaser. If he requests his oath, al-Qadi said: He does not have to take an oath; because he is a claimant (mudda'in), and the oath is upon the defendant (mudda'a 'alayhi). And because he has already admitted [the price] for him, so he is dispensed from the oath by the admission. The correct view is that he is obligated to take an oath that he does not know that, because he has claimed against him what necessitates the return of the merchandise or an increase in its price, so the oath is binding upon him, as in the agreed-upon case. He is not, in this instance, a claimant; rather, he is a defendant regarding the knowledge of the amount of the initial price. Then al-Khiraqi said: He has the right to make him swear that at the time he sold it, he did not know that its purchase price was more. This is correct, for if he had sold it at this price while knowing that its cost to him was more, the sale would be binding upon him according to what he contracted; because he engaged in the matter while knowing the circumstances, so it becomes binding upon him, like the purchaser of a defective item who knows of its defect. And since the sale becomes binding upon him through knowledge, then if he claims it against him, the oath becomes binding upon him. If he refuses, judgment is rendered against him. If he swears, the purchaser is given the choice between accepting it at the price plus the increase he erred with and deducting it from the profit, or rescinding the contract. [It is possible that if he sold it to him for one hundred with a profit of ten, then he later erred by ten, he is not required to deduct the ten from the profit; because the seller was satisfied with a profit of ten on this item, so he shall have no more than that. Likewise, if it becomes clear to him that he increased his capital, he does not decrease the profit from ten; because the seller did not sell it except for a profit of ten. But if he said: "I make a profit of one dirham on every ten," or said: "Ten for eleven" (dah yazdah), then he is required to deduct the ten from the profit in the case of error and the increase in the price in both scenarios.] We only established the option for him because he entered into the contract based on the price being one hundred and ten, so when it appeared to be more, there was harm to him in committing to it, so it is not binding upon him, like a defective item. If he chooses to take it for one hundred and twenty-one, the seller has no option; because he has given him an increase in benefit, so he has no option, like the seller of a defective item if the purchaser accepts it. And if the seller chooses to drop the increase for the purchaser, he also has no option; because he has offered it for the price upon which the contract was concluded, and they were mutually satisfied with it.

Section: It is permissible to sell by muwada'a (sale at a discount from the capital), which is for him to inform of his capital, then say: "I sold this to you"