Sahih Muslim 1002
صحيح مسلم#1002SahihA'isha reported that so far as these words of (Allah) Glorious and High are concerned:" And utter not thy prayer loudly, not be low in it" (xvii. 110) relate to supplication (du'a)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 4:164