Sahih Bukhari | Volume 4 | Hadith Number 748

Narrated by Anas
Allah's Apostle was neither very tall nor short, neither absolutely white nor deep brown. His hair was neither curly nor lank. Allah sent him (as an Apostle) when he was forty years old. Afterwards he resided in Mecca for ten years and in Medina for ten more years. When Allah took him unto Him, there was scarcely twenty white hairs in his head and beard.