Abu Huraira reported that the Prophet (sallallahu `alayhi wa sallam) said, 'Allah said:
My servant draws not near to Me with anything more loved by Me than the religious duties I have enjoined upon him, and My servant continues to draw near to Me with supererogatory works until I love him."'
[ Sahih Bukhari]
Niqaab is Mustahabb [Recommended]
The term mustahabb means ‘recommended’ i.e. something which is recommended to do because it draws a person closer to their Lord, their Creator and Sustainer. The above divine narration beautifully describes the way to seek the love of Allah. It is our service of Allah (subhaanahu wa ta'ala) through our obedience of whatever He has commanded us that draws us near to Him. And by doing more than what has been commanded to us, we may draw nearer to Him even more, something which every believer should strive for. When a Sister is already covering everything but her face and her hands, and she would like to do something extra to seek the love of Allah (subhaanahu wa ta'ala), the only things left for her to cover are her face and her hands.