Musnad Abu Ya'la al-Mawsili 155:181

Muhammad ibn al-Minhal, the brother of Hajjaj, narrated to us, Abu 'Awanah narrated to us, from 'Umar ibn Abi Salamah, from his father, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Change the gray hair, and do not resemble the Jews."