Musannaf Ibn Abi Shayba 33:427

Abu Usama narrated to us, from Ibn 'Awn, from Nafi', that Ibn 'Umar, when he would recite the Qur'an, disliked to speak, or he would not speak until he finished what he intended, or he would not speak until he finished, except for one day. I had taken the Mushaf for him while he was reciting, and he came upon a verse and said, "Do you know regarding what this was revealed?"