Musnad Ahmad 435:111

Marwan ibn Shuja’ narrated to us, he said: Khasif narrated to me, from Mujahid and ‘Ata’, from Ibn ‘Abbas, that Mu’awiyah informed him: That he saw the Messenger of Allah (may Allah bless him and grant him peace) "shorten some of his hair with a pair of scissors." I said to Ibn ‘Abbas: "Has this matter not reached us except from Mu’awiyah?" He said: "Mu’awiyah was not suspected regarding the Messenger of Allah (may Allah bless him and grant him peace)."