Khusayf (may Allah have mercy on him) narrates, through Mujahid and Ata', from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyiduna Mu'awiyah (may Allah be pleased with him) informed him: "He saw the Messenger of Allah (peace and blessings be upon him) have his hair shortened with an arrowhead." We said to Ibn Abbas (may Allah be pleased with them both): This has reached us only from Mu'awiyah. Ibn Abbas (may Allah be pleased with them both) said: Mu'awiyah was not suspected (of lying) about the Messenger of Allah (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16746