It was the practice of the Prophet (peace and blessings be upon him):
"He (peace and blessings be upon him) would command the dyeing of white hair, in opposition to the non-Arabs."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4887
Hadith Gradingالألبانی:حسن
Hadith Takhrij[طب] عن عتبة. الصحيحة ٢١١٤: ابن عساكر - أبي هريرة.