Musannaf Ibn Abi Shayba 16:1040

Abu Bakr narrated to us, he said: Shababa narrated to us, he said: Shu'bah narrated to us, from Abdullah ibn Dinar, from Ibn Umar, he said: The Messenger of Allah, may Allah bless him and grant him peace, forbade al-qaza' (shaving part of the head and leaving part of it).