Qur'an 24:60

وَٱلْقَوَٰعِدُ مِنَ ٱلنِّسَآءِ ٱلَّـٰتِى لَا يَرْجُونَ نِكَاحًا فَلَيْسَ عَلَيْهِنَّ جُنَاحٌ أَن يَضَعْنَ ثِيَابَهُنَّ غَيْرَ مُتَبَرِّجَـٰتٍۭ بِزِينَةٍ ۖ وَأَن يَسْتَعْفِفْنَ خَيْرٌ لَّهُنَّ ۗ وَٱللَّهُ سَمِيعٌ عَلِيمٌ

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.