Sunan an-Nasa'i Book 48, Hadith 29
The Messenger of Allah forbade plucking gray hairs.
"The Messenger of Allah said: 'O Ruwaifi', you may live for a long time after me, so tell the people that whoever ties up his beard, or twists it, or hangs an amulet, or cleans himself (after relieving himself) with animal dung or bones, Muhammad has nothing to do with him.'"
The Messenger of Allah said: "The Jews and Christians do not dye their hair, so be different from them."