Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

Zaid bin Thabit said, "When the Quran was compiled from various written manuscripts, one of the Verses of Surat Al-Ahzab was missing which I used to hear Allah's Apostle (SAW) reciting. I could not find it except with Khuzaima bin Thabit Al-Ansari, whose witness Allah's Messenger regarded as equal to the witness of two men. And the Verse was: "Among the believers are men who have been true their covenant with Allah..." (33.23)