Disagreement between buyer and seller

Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that the Prophet (peace and blessings be upon him) said: "If people were given (everything) on the basis of their claims, people would lay claim to the blood and the wealth of others; but the oath is upon the one against whom the claim is made."
Imam al-Shafi'i (may Allah have mercy on him) says: When two men transact the sale of a slave, and the seller says: I sold it for one thousand dirhams, and the buyer says: for 500 dirhams, the seller is claiming the higher price while the buyer is claiming the lower price; both will be made to take an oath, but it will begin with the seller.

Abd al-Rahman bin Qays bin Muhammad bin al-Ash'ath bin Qays narrates from his father, and he from his grandfather, that al-Ash'ath (may Allah be pleased with him) bought some slaves from the slaves of the khums from Abdullah (may Allah be pleased with him) for twenty thousand, and Abdullah (may Allah be pleased with him) sent someone to him to collect their price. Al-Ash'ath (may Allah be pleased with him) said: I took them for ten thousand. Abdullah (may Allah be pleased with him) said: Choose a man to judge between me and you. Al-Ash'ath (may Allah be pleased with him) said: You are (the judge) between me and yourself. Abdullah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When the two parties to a sale disagree and there is no proof between them, the word of the owner of the goods is accepted, or else they both abandon (the sale)."
This is a hasan (good), connected chain, and it has also been narrated through several ways with mursal chains which, when combined, make the hadith strong.

Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When the two parties to a sale disagree, the word of the seller is accepted, and the buyer has the option."

Awn bin Abdullah bin Utbah (may Allah have mercy on him) says that Sayyiduna Abdullah bin Mas'ud and Sayyiduna al-Ash'ath bin Qays (may Allah be pleased with them both) made a sale with each other. They disagreed about the price, so Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Appoint whomever you like as judge between me and you. Sayyiduna al-Ash'ath (may Allah be pleased with him) said: You yourself are the judge between me and yourself. Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: I will give the judgement that I heard from the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) said: "When the seller and the buyer disagree, the word of the seller is accepted, and the buyer has the option."
Awn bin Abdullah did not meet Abdullah bin Mas'ud, and this is a supporting witness for the previous report. Al-Shafi'i said: This hadith is munqati' (has a broken chain); I do not know anyone who narrates it with a connected chain from Ibn Mas'ud, and it has come through more than one way.

Abd al-Malik bin Umayr (may Allah have mercy on him) says: We were present with Abu Ubaydah bin Abdullah bin Mas'ud (may Allah have mercy on him) when two men came to him disputing about goods. One said: I took it for such-and-such, and the other said: I sold it for such-and-such. Abu Ubaydah (may Allah have mercy on him) said that matters of this kind used to come to Abdullah bin Mas'ud (may Allah be pleased with him), and Abdullah bin Mas'ud (may Allah be pleased with him) said: I was present with the Messenger of Allah (peace and blessings be upon him) when a similar matter came, and he (peace and blessings be upon him) asked the seller to take an oath, then gave the buyer the option: "(He may) take (the goods) or return them."

Likewise (through another chain).

It is narrated from one of the sons of Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When the two parties to a sale disagree and there is no witness between them, the seller will be asked to take an oath; then the buyer will have the option: if he wishes, he may take it, or return it."

Sa'id bin Maslamah (may Allah have mercy on him) mentions (it with the words): when there is no proof between the two parties to the sale.

Likewise (through another chain).
This hadith too is mursal; Abu Ubaydah did not meet his father.

Qasim (may Allah have mercy on him) narrates from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that Sayyiduna al-Ash'ath (may Allah be pleased with him) bought a slave from the slaves of the khums for 20 thousand, and Sayyiduna Abdullah (may Allah be pleased with him) sent someone to demand the price. Sayyiduna al-Ash'ath (may Allah be pleased with him) said: You sold it to me for 10 thousand. Either Sayyiduna al-Ash'ath (may Allah be pleased with him) had forgotten, or he found the price too high. Sayyiduna Abdullah (may Allah be pleased with him) said: I sold it for 20 thousand. Then Sayyiduna Abdullah (may Allah be pleased with him) said: Appoint some man between me and you. Sayyiduna al-Ash'ath (may Allah be pleased with him) said: I choose you to decide. He said: I will judge between you and me with the judgement I have heard from the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) said: "When the two parties to a sale disagree and there is no proof between them, the word of the owner of the goods is accepted, or else the two of them abandon the sale." Sayyiduna al-Ash'ath (may Allah be pleased with him) said: I abandon the sale, so he too abandoned it.
This is munqati' (has a broken chain).

Qasim bin Abd al-Rahman narrates from his father that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) sold Sayyiduna al-Ash'ath bin Qays (may Allah be pleased with him) a slave from the slaves of the government. The two of them (may Allah be pleased with them both) disagreed about the price. Sayyiduna Abdullah (may Allah be pleased with him) said: I sold you the slave for 20 thousand, and Sayyiduna al-Ash'ath (may Allah be pleased with him) said: I bought it for 10 thousand. Sayyiduna Abdullah (may Allah be pleased with him) said: If you wish, I will tell you a hadith of the Messenger of Allah (peace and blessings be upon him) which I heard from him (peace and blessings be upon him). Sayyiduna al-Ash'ath (may Allah be pleased with him) said: Bring it. He said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When the two parties to a sale disagree while the item sold is still present as it was, and there is no proof between them, the word of the seller is accepted, or else both of them abandon the sale." Sayyiduna al-Ash'ath (may Allah be pleased with him) said: I think the sale should be revoked.
(b) These are the words of Ibn Abi Shaybah's hadith. Ibn Abi Layla (may Allah have mercy on him) differed from the group in narrating this hadith: in its chain, where he said "from his father", and in its text, where he added: "while the item sold is still present as it was."
(c) Isma'il bin Ayyash narrated it from Musa bin Uqbah, from Muhammad bin Abd al-Rahman bin Abi Layla (may Allah have mercy on him), and said in it: "while the goods are just as they were," that is, in their original state.
When Isma'il narrates from the people of the Hijaz, he is not used as evidence; and Muhammad bin Abd al-Rahman bin Abi Layla, although great in fiqh, is da'if (weak) in narration because of his poor memory, his many errors in chains and texts, and his contradicting the hafiz scholars in them. May Allah forgive us and him. Al-Hasan bin Umarah followed him in this narration from al-Qasim, and he is matruk (abandoned) and not used as evidence.

Ibn Abi al-Zinad narrates from his father Abu al-Zinad (may Allah have mercy on him) that the jurists of the people of Madinah used to say: When two men make a sale and disagree about the price, both of them will be asked to take an oath. Whichever of the two refrains, the judgement will go against him. If both take the oath, the word of the seller is accepted and the buyer is given the option: if he wishes, he takes it at that price, otherwise he returns it.
(b) It is narrated from Qadi Shurayh (may Allah have mercy on him) that he said: If both of them refrain from the oath, the sale will be cancelled.