Abu Sa‘īd (may Allah be pleased with him) reported: The Messenger of Allah (ﷺ) once observed I‘tikāf (seclusion for worship) in the mosque, and he heard them reciting (the Qur’an) aloud. He lifted the curtain and said: "Indeed, each of you is conversing privately with his Lord, so let not one of you harm another, and let none of you raise his voice above another in recitation," or he said: "in prayer."
The Prophet (ﷺ) was staying in seclusion inside a tent within his mosque, seeking closeness to Allah. He (ﷺ) heard his Companions reciting the Qur’an aloud with such loud voices that they were disturbing one another. So he uncovered the curtain of his tent and reproached those who were doing that, saying: All of you are conversing privately with your Lord through your recitation of the Qur’an. Therefore, do not harm one another, and let none of you raise his voice above another in recitation or in prayer.