From Sahih Bukhari (Hadith 4784):
Narrated Zaid bin Thabit:When we collected the fragmentary manuscripts of the Qur'an into copies, I missed one of the Verses of Surat al-Ahzab which I used to hear Allah's Messenger (ﷺ) reading. Finally I did not find it with anybody except Khuza`ima Al-Ansari, whose witness was considered by Allah's Messenger (ﷺ) equal to the witness of two men. (And that Verse was:) 'Among the believers are men who have been true to their covenant with Allah
Reference: Bukhari 4784