It is narrated from Sayyiduna Anas bin Malik, Shu'ayb bin Amr and Najiyah bin Amr (may Allah be pleased with them) that they said: "We saw the Prophet (peace and blessings be upon him) dyeing (his hair)."
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7203