Narrated Ubaidullah bin Hafs:

that `Umar bin Nafi` told him that Nafi`, Maula `Abdullah had heard `Umar saying, "I heard Allah's Messenger (ﷺ) forbidding Al-Qaza'." 'Ubaidullah added: I said, "What is Al-Qaza'?" 'Ubaidullah pointed (towards his head) to show us and added, "Nafi` said, 'It is when a boy has his head shaved leaving a tuft of hair here and a tuft of hair there." Ubaidullah pointed towards his forehead and the sides of his head. 'Ubaidullah was asked, "Does this apply to both girls and boys?" He said, "I don't know, but Nafi` said, 'The boy.'" 'Ubaidullah added, "I asked Nafi` again, and he said, 'As for leaving hair on the temples and the back part of the boy's head, there is no harm, but Al-Qaza' is to leave a tuft of hair on his forehead unshaved while there is no hair on the rest of his head, and also to leave hair on either side of his head.'"

حَدَّثَنِي مُحَمَّدٌ، قَالَ أَخْبَرَنِي مَخْلَدٌ، قَالَ أَخْبَرَنِي ابْنُ جُرَيْجٍ، قَالَ أَخْبَرَنِي عُبَيْدُ اللَّهِ بْنُ حَفْصٍ، أَنَّ عُمَرَ بْنَ نَافِعٍ، أَخْبَرَهُ عَنْ نَافِعٍ، مَوْلَى عَبْدِ اللَّهِ أَنَّهُ سَمِعَ ابْنَ عُمَرَ ـ رضى الله عنهما ـ يَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَنْهَى عَنِ الْقَزَعِ‏.‏ قَالَ عُبَيْدُ اللَّهِ قُلْتُ وَمَا الْقَزَعُ فَأَشَارَ لَنَا عُبَيْدُ اللَّهِ قَالَ إِذَا حَلَقَ الصَّبِيَّ وَتَرَكَ هَا هُنَا شَعَرَةً وَهَا هُنَا وَهَا هُنَا‏.‏ فَأَشَارَ لَنَا عُبَيْدُ اللَّهِ إِلَى نَاصِيَتِهِ وَجَانِبَىْ رَأْسِهِ‏.‏ قِيلَ لِعُبَيْدِ اللَّهِ فَالْجَارِيَةُ وَالْغُلاَمُ قَالَ لاَ أَدْرِي هَكَذَا قَالَ الصَّبِيِّ‏.‏ قَالَ عُبَيْدُ اللَّهِ وَعَاوَدْتُهُ فَقَالَ أَمَّا الْقُصَّةُ وَالْقَفَا لِلْغُلاَمِ فَلاَ بَأْسَ بِهِمَا وَلَكِنَّ الْقَزَعَ أَنْ يُتْرَكَ بِنَاصِيَتِهِ شَعَرٌ، وَلَيْسَ فِي رَأْسِهِ غَيْرُهُ، وَكَذَلِكَ شَقُّ رَأْسِهِ هَذَا وَهَذَا‏.‏