Is there an illah in the hukm of Jilbab?

The following is translated from Arabic.

Question: Is the opinion regarding jilbaab qat'I because qardawi says 'Illah is modesty. Therefore, so as long as one is modestly attired jilbaab is not necessary?

Answer: Wearing the jilbaab is a hukm shar’i. It is wajib. Its daleel is qat’I but the Fuqaha differed over the description of ‘Idnaa’ (draping) in the ayah: ‘..to draw (idnaa) their jilbaabs over their bodies.’ So the jilbaab is definitely mentioned in the ayah but with regards to ‘idnaa’ (drawing or draping): some said it means draping it from the top of the head to the face and some said draping down the jilbaab means to the floor such that it covers the feet. And this is the preponderant view for us. As for those who said the texts regarding wearing the jilbaab has a ‘illah which is modesty and what’s important is that the woman should be modestly attired whether with jilbab or not. This is wrong.

This is because the texts regarding this issue do not have an ‘illah. So the woman who asked the Messenger (saw): O messenger of Allah, what about the one who does not have a jilbaab? He said: Let her wear the jilbaab of her sister’ ie let her borrow her sister’s jilbaab so that she can go out.’ The mafhoom of this is she should not go out without the jilbaab. This is an explicit text which has no ‘illah. The Messenger (saw) did not allow her to go out unless she wore a jilbaab.

As for what was mentioned in the ayah:

ذلك أدنى أن يعرفن فلا يؤذين

‘that they should be known so as not to be annoyed’[ahzab:59] This is the cause of revelation and not the ‘illah, which is to distinguish the free women from the slaves.

Therefore, wearing the jilbaab in the public life is fard on women regardless of her state.