Musnad Abu Ya'la al-Mawsili 111:101

Bishr ibn Sayhan narrated to us, Yazid ibn Zuray' narrated to us, from Sa'id ibn Abi 'Arubah, from Qatadah, from 'Ikrimah, from Ibn 'Abbas, from the Prophet (peace and blessings of Allah be upon him), who said: "The best thing with which you change gray hair is henna and katam."