Sahih Muslim Book 24, Hadith Number 5289.

Chapter : Disapproval of having a part of the head shaven and leaving part unshaved.

Ibn Umar reported that Allah’s Messenger (may peace be upon him) forbade Qaza. I said to Nafi: What is Qaza’? He said: This means having a part of a boy’s head shaved and leaving a part unshaven.