Sayyidah Maymunah bint Sa'd (may Allah be pleased with her) said: O Messenger of Allah, give us a ruling about the ritual bath (ghusl) for major impurity. He (peace and blessings be upon him) said: "Wet the roots of the hair and cleanse the skin thoroughly, for the example of those who do not perform the ritual bath well is like a tree on which water fell, yet neither did its leaves grow nor were its roots watered. So fear Allah and perform the ritual bath well, for it is part of the trust that has been placed upon you and of the secrets that have been entrusted to you." I said: O Messenger of Allah, how much water suffices for the head? He (peace and blessings be upon him) said: "Three handfuls."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21527