Musannaf Ibn Abi Shayba 3:4852

Waki’ narrated to us, he said: Hisham al-Dastawa’i narrated to us, from Qatadah, from Sa’id ibn al-Musayyib, he said: If there is someone with him who can recite, let them repeat it [the recitation], and he should not lead the prayer while looking at the Mushaf.