Musannaf Ibn Abi Shayba 3:2231

Abu Bakr narrated to us, he said: Hatim ibn Isma'il narrated to us, from 'Abdullah ibn Zayd, he said: I saw Anas ibn Malik praying the obligatory [prayer] in the Maqsura with 'Umar ibn 'Abd al-'Aziz, then he came out to us from it.