Sunan Abi Dawud Book 5, Hadith 80
The Prophet (ﷺ) went out at night and found AbuBakr praying in a low voice, and he passed Umar ibn al-Khattab who was raising his voice while praying.
When they both met the Prophet (ﷺ) together, the Prophet (ﷺ) said: I passed by you, AbuBakr, when you were praying in a low voice. He replied: I made Him hear with Whom I was holding intimate converse, Messenger of Allah. He (the Prophet) said to Umar: I passed by you when you were praying in a loud voice. He replied: Messenger of Allah, I was awakening the drowsy and driving away the Devil.
Al-Hasan added in his version: The Prophet (ﷺ) said: Raise your voice a little, AbuBakr, and he said to Umar: Lower your voice a little.
The Prophet's (ﷺ) recitation at night was partly in a loud voice and partly in a low voice.
Abu Dawud said: The name of Abu Khalid al-Walibi is Hurmuz.
Raise your voice a litte ; or he said to 'Umar: Lower your voice a little. But this version adds: (The Prophet said:) I heard you, Bilal, (reciting) ; you were reciting partly from this surah and partly from that surah. He said: This is all good speech ; Allah has combined one part with the other; The Prophet (ﷺ) said: All of you were correct.