Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 108
Narated By 'Abd al-Rahman al-Taimi : Ibn Abi Mulaikah was asked about ablution. He called for water. A vessel was then brought to him. He inclined it towards his right hand (poured water over it). He the put it in water; then he rinsed his mouth three times and cleansed his nose with water three times, and washed his face three times. He then put his hand in water and took it out; he then wiped his head and ears, in and out only once. He then washed his feet, and said: Where are those who ask me to perform ablution? I saw the Messenger of Allah (pbuh) performing ablution like that.
Abu Dawud said: All the sound traditions narrated by 'Uthman indicate that head is to be wiped once, because they mentioned (the washing of each part in) ablution three times. In their versions of the tradition they mentioned the wording: "he wiped his head." In this case they did not mention any number as they did in other cases.