Musannaf Ibn Abi Shayba 3:6203

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, who said: 'Abd al-Rahman ibn Yazid used to recite the Qur'an every seven [days]. Alqamah and al-Aswad used to recite it—one of them in five [days] and the other in six [days]. And Ibrahim used to recite it in seven [days].