Narrated Ibn Mas'ud:

That the Messenger of Allah ﷺ said: "When the two parties (in a deal) disagree then the seller's statement is taken as valid, and the purchaser retains the option."

[Abu 'Eisa said:] This Hadith is Mursal. 'Awn bin 'Abdullah did not see Ibn Mas'ud. This Hadith has also been reported from Al-Qasim bin 'Abdur-Rahman, from Ibn Mas'ud from the Prophet ﷺ. But it also Mursal.

[Abu 'Eisa said:] Ishaq bin Mansur said: "I said to Ahmad: what if when the two parties disagree and there is no proof (what is done)?' He said: 'The saying of the owner of the merchandise is taken as valid or they both refuse.' And Ishaq said as he did, and that in every case where his saying is taken, he must swear.'"

[Abu 'Eisa said:] Similar to this has been reported from some of the people of knowledge among the Tabi'in, Shuraih is among those.

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا سُفْيَانُ، عَنِ ابْنِ عَجْلاَنَ، عَنْ عَوْنِ بْنِ عَبْدِ اللَّهِ، عَنِ ابْنِ مَسْعُودٍ، قَالَ قَالَ رَسُولُ اللَّهِ ﷺ " إِذَا اخْتَلَفَ الْبَيِّعَانِ فَالْقَوْلُ قَوْلُ الْبَائِعِ وَالْمُبْتَاعُ بِالْخِيَارِ " .

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ مُرْسَلٌ عَوْنُ بْنُ عَبْدِ اللَّهِ لَمْ يُدْرِكِ ابْنَ مَسْعُودٍ . وَقَدْ رُوِيَ عَنِ الْقَاسِمِ بْنِ عَبْدِ الرَّحْمَنِ عَنِ ابْنِ مَسْعُودٍ عَنِ النَّبِيِّ ﷺ هَذَا الْحَدِيثُ أَيْضًا وَهُوَ مُرْسَلٌ أَيْضًا .

قَالَ أَبُو عِيسَى قَالَ إِسْحَاقُ بْنُ مَنْصُورٍ قُلْتُ لأَحْمَدَ إِذَا اخْتَلَفَ الْبَيِّعَانِ وَلَمْ تَكُنْ بَيِّنَةٌ قَالَ الْقَوْلُ مَا قَالَ رَبُّ السِّلْعَةِ أَوْ يَتَرَادَّانِ . قَالَ إِسْحَاقُ كَمَا قَالَ وَكُلُّ مَنْ كَانَ الْقَوْلُ قَوْلَهُ فَعَلَيْهِ الْيَمِينُ .

قَالَ أَبُو عِيسَى هَكَذَا رُوِيَ عَنْ بَعْضِ أَهْلِ الْعِلْمِ مِنَ التَّابِعِينَ مِنْهُمْ شُرَيْحٌ وَغَيْرُهُ نَحْوُ هَذَا .