Musnad Ahmad 27:1960

'Abd al-Samad and Abu Sa'id narrated to us, they said: 'Abdullah ibn al-Muthanna narrated to us, 'Abdullah ibn Dinar narrated to us, from Ibn 'Umar, who said: "The Messenger of Allah (may Allah bless him and grant him peace) forbade *al-qaza'*." 'Abd al-Samad said: "And *al-qaza'* is a patch [of hair left] on the head."