Musnad Ahmad 26:150

Waki’ narrated to us, Sufyan narrated to us, from Abu Ishaq, from Khumayr ibn Malik, who said: Abdullah said: "I recited seventy surahs from the mouth of the Messenger of Allah, may Allah bless him and grant him peace, and Zayd ibn Thabit has a lock of hair (braid) in the writing."