Musnad Ahmad 27:1166

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Ayyub, from Nafi', from Ibn 'Umar, that the Prophet, peace and blessings of Allah be upon him, saw a boy who had shaved part of his hair and left part of it. He forbade that and said: "Shave it all, or leave it all."