Yahya related to me from Malik from Yahya ibn Said that AbuQatada al-Ansari said to the Messenger of Allah, may Allah bless himand grant him peace, "I have a lot of hair which comes down to myshoulders, shall I comb it?'' The Messenger of Allah. may Allah blesshim and grant him peace, said, "Yes, and honour it." Sometimes AbuQatada oiled it twice in one day because the Messenger of Allah, mayAllah bless him and grant him peace, said to him. "Honour it."
USC-MSA web (English) reference: Book 51, Hadith 6
Arabic reference: Book 51, Hadith 1738