Ibn 'Umar (RA) reported that Allah's Messenger (ﷺ) forbade Qaza. I said to Nafi (RA) : What is Qaza'? He said: This means having a part of a boy's head shaved and leaving a part unshaven.
Hadith ReferenceSahih Muslim / The Book of Clothes and Adornment / Hadith: 2120