The Messenger of Allah ﷺ ruled that an oath together with a single witness is sufficient.Rabia said, "A son of Saad bin Ubada informed me, saying, 'We found in Saad's book that the Prophet ﷺ ruled with an oath together with a witness.'"
حدثنا يعقوب بن إبراهيم الدورقي حدثنا عبد العزيز بن محمد قال حدثني ربيعة بن أبي عبد الرحمن عن سهيل بن أبي صالح عن أبيه
قضى رسول الله ﷺ باليمين مع الشاهد الواحد قال ربيعة وأخبرني ابن لسعد بن عبادة قال وجدنا في كتاب سعد أن النبي ﷺ قضى باليمين مع الشاهد
[Its chain of transmission is sahih] Ibn Majah narrated it in "Rulings," in the chapter "Judgment Based on a Witness and an Oath," no. 2368, from Yaqub bin Ibrahim, through the same route, and Ibn Jarud graded it sahih, no. 1007.There are also narrations on this subject from Ali [to come, no. 1345], Jabir [to come, no. 1344], Ibn Abbas [Muslim, no. 1712], and Suraq [Ibn Majah, no. 2371].