Ubayy b. Ka'b reported that Allah's Messenger (ﷺ) said:The young man whom Khadir killed was a non-believer by his very nature and had he survived he would have involved his parents in defiance and unbelief.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، حَدَّثَنَا مُعْتَمِرُ بْنُ سُلَيْمَانَ، عَنْ أَبِيهِ، عَنْ رَقَبَةَ، بْنِ مَسْقَلَةَ عَنْ أَبِي إِسْحَاقَ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، عَنْ أُبَىِّ بْنِ كَعْبٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّ الْغُلاَمَ الَّذِي قَتَلَهُ الْخَضِرُ طُبِعَ كَافِرًا وَلَوْ عَاشَ لأَرْهَقَ أَبَوَيْهِ طُغْيَانًا وَكُفْرًا " .
Muslim
The Book of Destiny • Hadith 45