From those sins that many people belittle, and others are ignorant of their rulings, is dying one's hair black. Once when I was in Makkah, I saw a student of knowledge who used to dye his hair black. So I advised him to leave off this act, but he refused to do so and responded to me by saying: "This act is not haraam." This student had a friend who was a scholar, so I suggested (to the scholar) that he should advice him (the student of knowledge) concerning this affairs. He (the scholar) said to me: "It is not haraam, rather there's nothing wrong with doing so." I said: "What about the hadeeth of Jaabir in Saheeh Muslim which states:
..."but you should avoid making his hair black."