Musannaf Ibn Abi Shayba 3:5713

Waki’ narrated to us, he said: Shu’bah narrated to us, from Abu Bishr, from Sa’id ibn Jubayr, who said: When the Prophet (peace be upon him) would recite, he would raise his voice. This would please the Muslims and displease the disbelievers. He said: So [the verse] was revealed: "And do not recite [too] loudly in your prayer, nor recite [too] quietly."