Musannaf Ibn Abi Shayba 16:795

Abu Bakr narrated to us, he said: Shababa narrated to us, he said: Layth ibn Sa'd narrated to us, he said: Abu 'Ushayna al-Ma'afiri narrated to us, he said: I saw 'Uqba ibn 'Amir dyeing [his hair/beard] with black. And he would say: "We dye the tops of it, while the roots refuse [to change]."