Narrated Uncle of Umarah ibn Khuzaymah:

The Prophet ﷺ bought a horse from a Bedouin. The Prophet ﷺ took him with him to pay him the price of his horse. The Messenger of Allah ﷺ walked quickly and the Bedouin walked slowly. The people stopped the Bedouin and began to bargain with him for the horse as and they did not know that the Prophet ﷺ had bought it.

The Bedouin called the Messenger of Allah ﷺ saying: If you want this horse, (then buy it), otherwise I shall sell it. The Prophet ﷺ stopped when he heard the call of the Bedouin, and said: Have I not bought it from you? The Bedouin said: I swear by Allah, I have not sold it to you. The Prophet ﷺ said: Yes, I have bought it from you. The Bedouin began to say: Bring a witness. Khuzaymah ibn Thabit then said: I bear witness that you have bought it. The Prophet ﷺ turned to Khuzaymah and said: On what (grounds) do you bear witness?

He said: By considering you trustworthy, Messenger of Allah ﷺ! The Prophet ﷺ made the witness of Khuzaymah equivalent to the witness of two people.

حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى بْنِ فَارِسٍ، أَنَّ الْحَكَمَ بْنَ نَافِعٍ، حَدَّثَهُمْ أَخْبَرَنَا شُعَيْبٌ، عَنِ الزُّهْرِيِّ، عَنْ عُمَارَةَ بْنِ خُزَيْمَةَ، أَنَّ عَمَّهُ، حَدَّثَهُ وَهُوَ، مِنْ أَصْحَابِ النَّبِيِّ ﷺ أَنَّ النَّبِيَّ ﷺ ابْتَاعَ فَرَسًا مِنْ أَعْرَابِيٍّ فَاسْتَتْبَعَهُ النَّبِيُّ ﷺ لِيَقْضِيَهُ ثَمَنَ فَرَسِهِ فَأَسْرَعَ رَسُولُ اللَّهِ ﷺ الْمَشْىَ وَأَبْطَأَ الأَعْرَابِيُّ فَطَفِقَ رِجَالٌ يَعْتَرِضُونَ الأَعْرَابِيَّ فَيُسَاوِمُونَهُ بِالْفَرَسِ وَلاَ يَشْعُرُونَ أَنَّ النَّبِيَّ ﷺ ابْتَاعَهُ فَنَادَى الأَعْرَابِيُّ رَسُولَ اللَّهِ ﷺ فَقَالَ إِنْ كُنْتَ مُبْتَاعًا هَذَا الْفَرَسَ وَإِلاَّ بِعْتُهُ . فَقَامَ النَّبِيُّ ﷺ حِينَ سَمِعَ نِدَاءَ الأَعْرَابِيِّ فَقَالَ " أَوَلَيْسَ قَدِ ابْتَعْتُهُ مِنْكَ " . فَقَالَ الأَعْرَابِيُّ لاَ وَاللَّهِ مَا بِعْتُكَهُ . فَقَالَ النَّبِيُّ ﷺ " بَلَى قَدِ ابْتَعْتُهُ مِنْكَ " . فَطَفِقَ الأَعْرَابِيُّ يَقُولُ هَلُمَّ شَهِيدًا . فَقَالَ خُزَيْمَةُ بْنُ ثَابِتٍ أَنَا أَشْهَدُ أَنَّكَ قَدْ بَايَعْتَهُ . فَأَقْبَلَ النَّبِيُّ ﷺ عَلَى خُزَيْمَةَ فَقَالَ " بِمَ تَشْهَدُ " . فَقَالَ بِتَصْدِيقِكَ يَا رَسُولَ اللَّهِ . فَجَعَلَ رَسُولُ اللَّهِ ﷺ شَهَادَةَ خُزَيْمَةَ بِشَهَادَةِ رَجُلَيْنِ .