Amr bin Shu'aib narrated from his father that the Prophet ﷺ said regarding testimony: "If (the claimant) brings one witness, then he should also swear an oath along with the witness (then the decision will be in his favor)."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1717
Hadith Takhrijاسناده ضعيف لإرساله ولضعف مسلم بن خالد ولعنعنة ابن جريج : اخرجه البيهقي : 10/ 172 - وفى المعرفة السنن والآثار له (5919)۔