Musnad Abu Ya'la al-Mawsili 9:5

Narrated to us Abd al-Rahman ibn Salih, narrated to us Muhammad ibn Fudayl, from Isma'il ibn Abi Khalid, from Abu Juhayfah, who said: I saw the Prophet, may Allah bless him and grant him peace, and I said: "Describe him to me." He said: "White, having gray hair."