Mishkat al-Masabih — Hadith #37648

Abu Qatada said God’s Messenger went out one night and found Abu Bakr praying in a low voice, and he passed ‘Umar who was raising his voice while praying. When they both were with the Prophet he said, “I passed you, Abu Bakr, when you were praying in a low voice.” He replied, “I made Him hear with whom I was holding intimate converse, Messenger of God.” He said to ‘Umar, “I passed you when you were raising your voice while praying.” He replied, “Messenger of God, I was wakening the drowsy and driving away the devil.” The Prophet said, “Raise your voice a little, Abu Bakr;” and he said to ‘Umar, “Lower your voice a little.” Abu Dawud transmitted it, and Tirmidhi transmitted something similar.