Mishkat al-Masabih
Ibn ‘Umar told that when 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 al or leave it all." Muslim transmitted it.
وَعَنِ ابْنِ عُمَرَ: أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَأَى صَبِيًّا قَدْ حُلِقَ بَعْضُ رَأْسِهِ وَتُرِكَ بَعْضُهُ فَنَهَاهُمْ عَنْ ذَلِكَ وَقَالَ: «احْلِقُوا كُلَّهُ أَوِ اتْرُكُوا كُلَّهُ» . رَوَاهُ مُسْلِمٌ
Reference