Musannaf Ibn Abi Shayba 3:6453

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Isra’il, from Jabir, from ‘Amir, Muhammad bin ‘Ali, ‘Ata’, Tawus, al-Qasim, and Mujahid; they said: There is no harm in a man praying the obligatory prayer and others while in his sleeve are tablets and a scroll containing poetry and things similar to it.