Chapter 40: The Book of Greetings
' A' isha reported that the wives of Allah' s Messenger (ﷺ) used to go out in the cover of night when they went to open fields (in the outskirts of Medina) for easing themselves. 'Umar b Khattab used to say: Allah' s Messenger, ask your ladies to observe veil, but Allah' s Messenger (ﷺ) did not do that. So there went out Sauda, daughter of Zarn' a, the wife of Allah' s Messenger (ﷺ), during one of the nights when it was dark. She was a tall statured lady. 'Umar called her saying: Sauda, we recognise you. (He did this with the hope that the verses pertaining to veil would be revealed.) 'A' isha said: Allah, the Exalted and Glorious, then revealed the verses pertaining to veil.
Sahih Muslim 2170d