Mishkat al-Masabih 22 Clothing كتاب اللباس 116

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

Ibn ‘Umar told that when the Prophet 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.