(1) The Book of Purification
كتاب الطهارة
(4) Chapter: Ablution (Wudu)
(4) باب الوضوء
Bulugh al-Maram 34 
Narrated ‘Ali (rad) regarding the description of the ablution of the Prophet (ﷺ):
He (the Prophet) wiped his head (with water) only once. [Reported by Abu Da’ud, An-Nasa’i, AtTirmidhi with a Sahih Sanad (authentic chain of narrators). At-Tirmidhi said, “It’s the most Hadith on this subject”].
وَعَنْ عَلِيٍّ ‏- رضى الله عنه ‏- ‏-فِي صِفَةِ وُضُوءِ اَلنَّبِيِّ صَلَّى اَللَّهُ عَلَيْهِ وَسَلَّمَ‏- قَالَ: { وَمَسَحَ بِرَأْسِهِ وَاحِدَةً.‏ } أَخْرَجَهُ أَبُو دَاوُد َ 1‏ .‏


‏1 ‏- صحيح.‏ رواه أبو داود (111)‏.‏

Reference : Bulugh al-Maram 34
In-book reference : Book 1, Hadith 39
English translation : Book 1, Hadith 38