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." 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. 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.'" Similar to this has been reported from some of the people of knowledge among the Tabi'in, Shuraih is among those.