Musnad Ahmad 27:1530

Abu Ja'far al-Mada'ini narrated to us, Mubarak ibn Fudalah informed us, from Abdullah ibn Dinar, from Abdullah ibn Umar, that he narrated to him, saying: "The Messenger of Allah, peace and blessings of Allah be upon him, forbade al-qaza' (shaving part of the head and leaving part)." [Abdullah ibn Ahmad said]: I found in my father's book in his own handwriting: Husayn narrated to me, he said: al-Mubarak narrated to us, from Ubaydullah ibn Umar, that Abdullah ibn Dinar narrated to him, that Abdullah ibn Umar narrated to him, saying: "The Messenger of Allah, peace and blessings of Allah be upon him, forbade al-qaza'."