An-Nur - 24:60

وَالْقَوَاعِدُ مِنَ النِّسَاء اللَّاتِي لَا يَرْجُونَ نِكَاحًا فَلَيْسَ عَلَيْهِنَّ جُنَاحٌ أَن يَضَعْنَ ثِيَابَهُنَّ غَيْرَ مُتَبَرِّجَاتٍ بِزِينَةٍ وَأَن يَسْتَعْفِفْنَ خَيْرٌ لَّهُنَّ وَاللَّهُ سَمِيعٌ عَلِيمٌ
[24:60]
And (as for) women advanced in years who do not hope for a marriage, it is no sin for them if they put off their clothes without displaying their ornaments; and if they restrain themselves it is better for them; and Allah is Hearing, Knowing.
Such elderly women as are past the prospect of marriage,- there is no blame on them if they lay aside their (outer) garments, provided they make not a wanton display of their beauty: but it is best for them to be modest: and Allah is One Who sees and knows all things.
As for women past child-bearing, who have no hope of marriage, it is no sin for them if they discard their (outer) clothing in such a way as not to show adornment. But to refrain is better for them. Allah is Hearer, Knower.