Sayyiduna Anas (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When a woman takes the ritual bath after her menstruation, she should undo her hair and wash it with khitmi and ushnan (cleansing plants), and when she takes the ritual bath for janabah, she should not undo her head nor wash it with khitmi and ushnan."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 863