مختصر صحيح مسلم
Mukhtasar Sahih Muslim
Exegesis of the Noble Quran
Allah’s saying: "Do not recite your prayer loudly..." (Tafsir Al-Isra, Bani Isra'il)
Umm al-Mu’minin Aisha Siddiqa (may Allah be pleased with her) says regarding the statement of Allah Almighty: (And do not recite your prayer too loudly...) that this was revealed about supplication (i.e., do not supplicate in a very loud voice nor in a very low voice).