Musnad Abu Ya'la al-Mawsili 155:161

And from al-Awza'i, from al-Zuhri, he said: Abu Salamah ibn 'Abd al-Rahman and Sulayman ibn Yasar narrated to me, from Abu Hurayrah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, the Jews and the Christians do not dye [their hair/beards], so differ from them."