Mishkat al-Masabih 4291

Thabit told that when Anas was asked whether the Prophet dyed his hair he replied, "If I had wanted to count the hoary hairs which were on his head I could have done so,” adding that he did not dye his hair. In a version he added that Abu Bakr dyed his hair with henna and katam, and ‘Umar dyed it with henna alone. (Bukhari and Muslim.)