Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The matter of Hijab is discussed in this verses: "And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.) and not to show off their adornment except only that which is apparent (like palms of hands or one eye or both eyes for necessity to see the way, or outer dress like veil, gloves, head-cover, apron, etc.), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) (An-Nur 24:31)
It is also mentioned in Surah Al-Ahzab: "O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way). That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allâh is Ever OftForgiving, Most Merciful. (Al-Ahzab 33:59)
The above verses clearly prove that every Muslim woman is addressed and ordered to observe Hijab. It was not peculiar to the wives of the Prophet (Sallallahu Alaihi wa Sallam).
Know that the order of Hijab was revealed in
Allah knows best.