The Lawsonia inermis, or Eastern privet, used for dying the hands and feet on festive occasions [MARRIAGE.] Muhammad enjoined the use of hinna’, and approved of women staining their hands and feet with it. He also dyed his own beard with it, and recommended its use for this purpose (Mishkat, book xx. c. 4.) It has therefore become a religious custom and is sunnah.
Based on Hughes, Dictionary of Islam