Musannaf Ibn Abi Shayba 13:258

Waki’ narrated to us, he said: Sufyan narrated to us, from Abu Hasin, from Abu al-Duha, he said: I asked Shurayh, Masruq, and Abdullah ibn Yazid about the selling of copies of the Mushaf (Qur’an). They said: We do not take a price for the Book of Allah.