Silsilah as-Sahihah 519 — Prayer is whispering to Allah; how loud

It is narrated from a man of the tribe of Banu Bayadah that the Messenger of Allah (peace and blessings be upon him) observed i'tikaf during one ten-day period of Ramadan and said: "When one of you is praying, he is whispering to his Lord, so do not recite the Qur'an aloud (in prayer), for in this way you cause discomfort to other believers."