This was revealed concerning supplication.
في قوله عزوجل: {ولا تجهر بصلاتك ولا تخافت بها}
أنزل هذا في الدعاء.
No references are available.
Bukhari related it in the tafsir (4723), and Muslim in the prayer (447), both of them through Hisham bin Urwa, from his father, from Ayesha, who narrated it. The wording given is Muslim's.