Musnad Ahmad 3:71

Ishaq ibn Isa narrated to us, Abd al-Rahman ibn Abi al-Zinad narrated to us (H), and Surayj and Husayn said: Ibn Abi al-Zinad narrated to us, from his father, from Amir ibn Sa’d—Husayn said: Ibn Abi Waqqas—who said: I heard Uthman ibn Affan saying: "Nothing prevents me from narrating from the Messenger of Allah, may Allah bless him and grant him peace, [the fact] that I am not the most retentive of his companions regarding him. But I bear witness that I heard him say: 'Whoever says about me what I have not said, let him take his seat in the Fire.'" Husayn said: "The most retentive of his companions regarding him."