Sunan Abi Dawud Book 5, Hadith 81
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.
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.
A man got up at night and recited the Qur'an in a loud voice. When the dawn came, the Messenger of Allah (ﷺ) said: May Allah have mercy on so-and-so who reminded me many verses that I had nearly forgotten.
Abu Dawud said: Harun al-Nahwi transmitted from Hammad b. Salamah the Quranic verse of Surah Al-'Imran: "How many of the prophet fought (in Allah's way)" (3:146)