It is narrated from Sayyiduna al-Nu'man bin Bashir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) bought a horse from a Bedouin, but the Bedouin went back (on his word) and began to deny the deal. Upon this, Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) came and said: "O Bedouin, are you denying (the deal)? I bear witness against you that you sold this horse to him (peace and blessings be upon him)." The Bedouin said: "If Khuzaymah bin Thabit bears witness against me, then (I accept it; now) give me my price." Then the Messenger of Allah (peace and blessings be upon him) asked (in surprise): "O Khuzaymah, we did not make you a witness (at the time), so how are you bearing witness?" He said: "I fully affirm you (peace and blessings be upon him) regarding the news of the heavens (revelation); shall I not affirm what you (peace and blessings be upon him) say regarding this Bedouin?" So the Messenger of Allah (peace and blessings be upon him) made his single testimony equal to the testimony of two men.
In the history of Islam there was no person other than Sayyiduna Khuzaymah bin Thabit (may Allah be pleased with him) whose single testimony was made to stand in place of the testimony of two men and was legally accepted.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب المناقب / 4020
Hadith Gradingمحدثین:إسناده ضعيف جدًا
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :إسناده ضعيف جدًا » «أخرجه سنن أبي داود برقم: 3607، وأخرجه مسند أحمد برقم: 21376، وأخرجه فتح الباري برقم: 4506، وأخرجه مصنف عبد الرزاق برقم: 15566، وأخرجه المستدرك على الصحيحين برقم: 2233»