From Sahih Bukhari (Hadith 2807):
Narrated Kharija bin Zaid:Zaid bin Thabit said, "When the Qur'an was compiled from various written manuscripts, one of the Verses of Surat Al-Ahzab was missing which I used to hear Allah's Messenger (ﷺ) reciting. I could not find it except with Khuza`ima bin Thabit Al-Ansari, whose witness Allah's Messenger (ﷺ) regarded as equal to the witness of two men. And the Verse was:-- "Among the believers are men who have been true to what they covenanted with Allah
Reference: Bukhari 2807