Silsilat al-Ahadith al-Sahihah

When Anas bin Malik (may Allah be pleased with him) was asked about the dyeing (of hair) of the Messenger of Allah (peace and blessings be upon him), he said: Only a few hairs of the Messenger of Allah (peace and blessings be upon him) had turned white, however, after him, Abu Bakr and Umar (may Allah be pleased with them both) used henna and katam (a plant) for dyeing. (It should also be remembered that) when Abu Bakr (may Allah be pleased with him) brought his father Abu Quhafa (may Allah be pleased with him) to the Messenger of Allah (peace and blessings be upon him) on the day of the conquest of Makkah, the Prophet (peace and blessings be upon him) said to Abu Bakr (may Allah be pleased with him): "If you had left the elder at his place, we would have gone to him out of respect for Abu Bakr." Then he accepted Islam, and his beard and head hair were white like the thaghamah plant. The Messenger of Allah (peace and blessings be upon him) said: "Change the color of both (i.e., the beard and the head hair) and avoid black color."