Is it obligatory to wash the hair after sexual intercourse for the ghusl to be valid?

Washing the hair during ghusl (ritual bath) after major impurity (janabah) is obligatory for both men and women. Water must reach the roots of the hair, even if it is thick. The proof for this is that the Prophet, peace and blessings be upon him, would run his fingers through the roots of his hair until they were thoroughly wet, and then pour three handfuls of water over his head. As for a woman undoing her braided hair, it is not obligatory during ghusl after janabah or menstruation; it suffices for her to pour three handfuls of water over her head, due to the hardship involved in undoing it.