Musannaf Ibn Abi Shayba 16:817

Abu Bakr narrated to us, he said: Abu Usamah narrated to us, from Ubayd Allah, from Sa'id ibn Abi Sa'id, that Ibn Jurayj asked Ibn Umar, saying: "I saw you dyeing your beard yellow with wars." Ibn Umar said: "As for my dyeing my beard yellow, I saw the Messenger of Allah, may Allah bless him and grant him peace, dyeing his beard yellow."