It was narrated from 'Aishah that the Messenger of Allah (ﷺ) used to soak his head, then he would pour water over it three times.
Sunan an-Nasa'i Book 1, Hadith 250
← Previous Hadith 'Aishah narrated concerning the Ghusl of the Prophet (ﷺ) from Janabah, that he used to wash his hands and perform Wudu', then he would run (his fingers) through his (hair on his) head so that it reaches all of his hair, then he would pour water over his entire body.

Sunan an-Nasa'i Book 1, Hadith 249 Next Hadith → "They argued about Ghusl in the presence of the messenger of Allah (ﷺ). One of the people said: 'I perform Ghusl in such-and-such a manner.' The Messenger of Allah (ﷺ) said: 'As for me, I pour three handfuls of water over my head.'"

Sunan an-Nasa'i Book 1, Hadith 251