Sunan an-Nasa'i, Hadith 426 ⓘ
It was narrated that Jabir said: "When the Messenger of Allah performed Ghusl, he would pour water on his head three times."
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ شُعْبَةَ، عَنْ مُخَوَّلٍ، عَنْ أَبِي جَعْفَرٍ، عَنْ جَابِرٍ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا اغْتَسَلَ أَفْرَغَ عَلَى رَأْسِهِ ثَلاَثًا .
also referenced under: Book 4, Hadith 31 (In-Book) & Volume 1, Book 4, Hadith 426 (DarusSalam)