The Prophet (ﷺ) saw a boy with part of his head shaved and part left unshaven. He forbade them to do that, saying: Shave it all or leave it all.
Sunan Abi Dawud Book 35, Hadith 37
← Previous Hadith the Prophet (ﷺ) forbade qaza' which means that the head of a boy is shaved and a lock is left.

Sunan Abi Dawud Book 35, Hadith 36 Next Hadith → I had a hanging lock of hair. My mother said to me: I shall not cut it, for the Messenger of Allah (ﷺ) used to stretch it our and hold it.

Sunan Abi Dawud Book 35, Hadith 38