Aisha, wife of the Prophet, reported:

Aisha, wife of the Prophet, reported: When the Prophet, peace and blessings be upon him, took a bath after intercourse, he began by washing his hands and then he would perform an ablution as if for prayer; then, he would put his fingers in the water and wash the roots of his hair with them, and then he would pour three handfuls of water over his head and pour water all over his body.

Source: Sahih Bukhari 245

Grade: Sahih (authentic) according to Al-Bukhari

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَانَ إِذَا اغْتَسَلَ مِنْ الْجَنَابَةِ بَدَأَ فَغَسَلَ يَدَيْهِ ثُمَّ يَتَوَضَّأُ كَمَا يَتَوَضَّأُ لِلصَّلَاةِ ثُمَّ يُدْخِلُ أَصَابِعَهُ فِي الْمَاءِ فَيُخَلِّلُ بِهَا أُصُولَ شَعَرِهِ ثُمَّ يَصُبُّ عَلَى رَأْسِهِ ثَلَاثَ غُرَفٍ بِيَدَيْهِ ثُمَّ يُفِيضُ الْمَاءَ عَلَى جِلْدِهِ كُلِّهِ

245 صحيح البخاري كِتَاب الْغُسْل بَاب الْوُضُوءِ قَبْلَ الْغُسْلِ