Narrated `Umar:
I said, "O Allah's Messenger (ﷺ)! Good and bad persons enter upon you, so I suggest that you order the mothers of the Believers (i.e. your wives) to observe veils." Then Allah revealed the Verses of Al- Hijab.
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 313
Arabic reference: Book 65, Hadith 4790