Musannaf Ibn Abi Shayba 3:6183

Waki’ narrated to us, he said: Sufyan narrated to us, from al-A’mash, from Khaythama, who said: I entered upon ‘Abdullah ibn ‘Amr while he was reading from the Mushaf. He said: "This is my hizb (portion) which I intend to stand [in prayer] with tonight."