Sahih al-Bukhari 6327

Arabic

حَدَّثَنَا عَلِيٌّ، حَدَّثَنَا مَالِكُ بْنُ سُعَيْرٍ، حَدَّثَنَا هِشَامُ بْنُ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، ‏{‏وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا‏}‏ أُنْزِلَتْ فِي الدُّعَاءِ‏.‏

English translation

Narrated `Aisha:The Verse: 'Neither say your prayer aloud, nor say it in a low tone.' (17.110) was revealed as regards invocation

Reference: Sahih al-Bukhari 6327, Book of Invocations. English translation by Dr. Muhammad Muhsin Khan.