Al-Matalib al-'Aliyah 3683 — Surah al-Ahzab

It is narrated from Bajalah al-Tamimi (may Allah have mercy on him) that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saw a copy of the Qur'an (mushaf) in the lap of a slave boy of his, in which was written: "The Prophet is closer to the believers than their own selves, and he is a father to them, and his wives are their mothers" [Surah al-Ahzab: 6]. So Sayyiduna Umar (may Allah be pleased with him) said (on seeing the extra words in it): "O boy! Erase it." He replied: "I will never erase it, for it is written this way in the mushaf of Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) as well." So Sayyiduna Umar (may Allah be pleased with him) went to Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) (to verify it), and he replied (promptly): "The memorisation and study of the Noble Qur'an kept me occupied, while buying and selling and trade in the markets kept you busy, when you used to go about at the door of Ibn al-Ajma' carrying (the burden of) your handmill on your neck."
This chain is sahih on the condition of al-Bukhari.