Silsilat al-Ahadith al-Sahihah

Sayyiduna Anas bin Malik (may Allah be pleased with him) says: Some Jews came to the Messenger of Allah (peace and blessings be upon him). He inquired about them. The Companions (may Allah be pleased with them) said: O Messenger of Allah! These are Jews and they do not dye their hair. The Prophet (peace and blessings be upon him) said: "Change the sign of the Jews, but do not change it with black color."