Is it permissible for me to dye my hand with a black dye that is used in dyeing gray hair?
All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Dyeing can be made by using henna, katam, saffron, waris (safflower), black due and the like. It is recommended to use henna or katam, or both, in dyeing. It is disliked, and maybe prohibited according to some views, to dye gray hair black in cases other than wars, for the general indication of the reports that signify that. It is recommended for a married woman to dye the palms of her hands and legs with henna or the like of other forms of dyeing so as to adorn them.
Dhamrah ibn Sa‘eed reported from his grandmother, who reported from a woman who had prayed towards the two Qiblahs (direction of prayer) along with the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, that she said: "Once, the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, entered upon me and said: 'Dye your hands, one of you leaves dyeing until her hand becomes like that of a man!'" He said: "She never left it until she passed away. She used to do this even when she was eighty years old." [Ahmad]
As for an unmarried woman, it is disliked for her to use dyeing, for there is no need for that, and out of fear of temptation that may be caused. This is the opinion of the majority of scholars.
There is nothing wrong with dyeing hands black if it is a usual means by which women adorn themselves for their husbands and as long as it does not imply imitating non-Muslim or immoral women and is not a motto for an invalid belief. Dyeing has no effect on ablution as long as its substance is removed. That is because what remains, after removing its substance, is just a color and color has no effect at all since it does not prevent water from reaching the skin.
Allaah Knows best.
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