Musnad Ahmad 27:449

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Ayyub, from Nafi', from Ibn 'Umar, that the Prophet (peace and blessings of Allah be upon him) said on the day of al-Hudaybiyyah: "O Allah, forgive those who shave." A man said: "And those who shorten?" He said: "O Allah, forgive those who shave." He said: "And those who shorten," until he said it three or four times. Then he said: "And those who shorten."