Abd al-Rahman bin Buzurj said: "I saw the two sons of Sayyidah Fatimah (may Allah be pleased with her), Sayyiduna al-Hasan and Sayyiduna al-Husayn (may Allah be pleased with them both), dyeing their hair black, and Sayyiduna al-Husayn used to leave the hair below his lower lip (the 'anfaqah) undyed."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2774