Umara bin Khuzayma reported,

His uncle, who was one of the companions of the Prophet ﷺ, related to him that the Prophet ﷺ bought a horse from an Arabi. The Prophet ﷺ asked him to follow him so he could pay him the price of his horse. The Prophet ﷺ walked quickly, while the Arabi lagged behind. Some men began stopping the Arabi and bargaining with him over the horse, not realizing that the Prophet ﷺ had already bought it. The Arabi then called out to the Messenger of Allah ﷺ, saying, "If you are buying this horse, then take it. Otherwise, I will sell it to someone else."When the Prophet ﷺ heard the Arabi's call, he stood up and said, "Have I not already bought it from you?"The Arabi replied, "No, by Allah, I have not sold it to you."The Prophet ﷺ said, "Yes, I have indeed bought it from you."The Arabi began saying, "Bring a witness."Khuzayma bin Thabit said, "I bear witness that you sold it to him."The Prophet ﷺ turned to Khuzayma and asked, "On what basis do you bear witness?"He replied, "By affirming your truthfulness, Messenger of Allah."So the Prophet ﷺ counted Khuzayma's testimony as the testimony of two men.

عن عمارة بن خزيمة

أن عمه حدثه، وهو حدثه، وهو من أصحاب النبي ﷺ أن النبي ﷺ ابتاع فرسا من أعرابي، فاستتبعه النبي ﷺ ليقضيه ثمن فرسه، و أسرع النبي ﷺ المشي، وأبطأ الأعرابي، فطفق رجال يعترضون الأعرابي فيساومونه بالفرس، ولا يشعرون أن النبي ﷺ ابتاعه، فنادى الأعرابي رسول الله ﷺ فقال: إن كنت مبتاعا هذا الفرس وإلا بعته فقام النبى ﷺ حين سمع نداء الأعرابي فقال: أوليس قد ابتعته منك؟ فقال الأعرابي: لا والله ما بعتك. فقال النبي ﷺ: بلى قد ابتعته منك. فطفق الأعرابي يقول: هلم شهيدا. فقال خزيمة بن ثابت: أنا أشهد أنك قد بايعته فأقبل النبي ﷺ على خزيمة، فقال: بم تشهد؟ فقال: بتصديقك يا رسول الله، فجعل النبي ﷺ شهادة خزيمة بشهادة رجلين.