An elderly man of the Ansar, one of the companions of the Prophet ﷺ, related to him that the Messenger of Allah ﷺ said, regarding the verse "And do not be loud in your prayer" [Isra 17:110], that this concerns supplication. Do not raise your voice in supplication, for you may mention your sins, and someone may hear them from you and then reproach you for them.
أن شيخا من الانصار من أصحاب النبي ﷺ حدثه أن رسول الله ﷺ قال: {ولا تجهر بصلاتك} ذلك في الدعاء، لا ترفع صوتك في الدعاء، فتذكر ذنوبك، فيسمع منك، فتعير بها.
No references are available.
Bukhari narrated it in Tarikh al-Kabir (3/256), saying, Asbagh said, from Ibn Wahb, who said, Amr told us, from Darraj, and he mentioned it.Its chain of transmission is hasan because of Darraj, for his hadith is hasan except regarding Abu Haytham. Asbagh is the son of Faraj, the Egyptian, one of the senior teachers of Bukhari, and Bukhari narrated from him in several places in his Sahih. So his saying, "Asbagh said," is to be taken as indicating a connected chain.