Musnad Ahmad 435:112

Abdullah ibn Ahmad said: Ibrahim ibn Abdullah ibn Bashar al-Wasiti narrated to us, Mu’ammal and Abu Ahmad—or one of them—narrated to us, from Sufyan, from Ja’far ibn Muhammad, from his father, from Ibn Abbas, from Mu’awiyah, that the Prophet, peace and blessings of Allah be upon him, shortened [his hair] with a *mishqas* (a broad-headed arrow).