What did Allah (swt) reveal to Prophet Muhammad (saw) in response to Umar's suggestion regarding the wives of the Believers observing veils?
 Narrated `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.