Sunan an-Nasa'i 4648
سنن النسائي#4648SahihAbdullah said:"I heard the Messenger of Allah say: 'If the two parties to a transaction disagree, and neither of them has any proof, then it is as the owner of the goods says, or they may cancel it
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 44:200