Sahih Al Bukhari – Book of Prophetic Commentary On The Qur'an (Tafseer Of The Prophet (pbuh))

Volumn 006, Book 060, Hadith Number 313.
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Narated By Umar : I said, "O Allah's Apostle! 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.