There were not even twenty white hairs on the head and beard of the Messenger of Allah ﷺ. Abu Bakr dyed his hair with henna and katam, and Umar dyed his with henna.
حدثنا معتمر عن حميد
لم يكن في رأس رسول الله ﷺ ولحيته عشرون شعرة بيضاء وخضب أبو بكر بالحناء والكتم وخضب عمر بالحناء
Its chain of transmission is sahih. Bukhari narrated the hadith in 6/564, no. 3547, Fath, in the book of virtues, on the description of the Prophet ﷺ, and Muslim in 4/1824, no. 2347, in the book of virtues, on the graying of the Prophet's hair ﷺ, and many others besides them.