Musannaf Ibn Abi Shayba 3:5723

Hashim ibn al-Qasim narrated to us, he said: Abu Sa’id narrated to us, he said: Salim narrated to us, from Sa’id, regarding [the verse]: "And do not recite [your prayer] loudly or whisper it." He said: The Prophet, peace and blessings of Allah be upon him, used to raise his voice with "In the name of Allah, the Most Gracious, the Most Merciful." Musaylimah had named himself "the Rahman" (the Most Gracious). When the polytheists heard that from the Prophet, peace and blessings of Allah be upon him, they said: "He has mentioned Musaylimah, the god of Yamama." Then they opposed him with whistling, clapping, and shouting. So Allah the Exalted revealed: "And do not recite [your prayer] loudly or whisper it."