Musnad Ahmad 435:43

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj informed us, and Rawh said: Ibn Jurayj narrated to us, he said: Al-Hasan ibn Muslim informed me, from Tawus, from Abdullah ibn Abbas, that Muawiyah ibn Abi Sufyan—Rawh said: informed him—said: "I shortened [the hair of] the Messenger of Allah, peace and blessings of Allah be upon him, with a *mishqas* (a broad-headed arrow) at Al-Marwah, or I saw him shortening it with a *mishqas* at Al-Marwah."