Q 18:76

Then they both proceeded till they met a boy, and he (Khidr) killed him. Musa said: "Have you killed an innocent person without Nafs? Verily, you have committed a thing Nukr! (74)He said: "Did I not tell you that you can have no patience with me? (75)He said: "If I ask you anything after this, keep me not in your company, you have received an excuse from me. (76) The Story of killing the Boy فَانطَلَقَا (Then they both proceeded,) means, after the first incident, حَتَّىٰ إِذَا لَقِيَا غُلَامًا فَقَتَلَهُ (till they met a boy, and he (Khidr) killed him.) It has been stated previously that this boy was playing with other boys in one of the towns, and that Al-Khidr deliberately singled him out. He was the finest and most handsome of them all, and Al-Khidr killed him. When Musa, peace be upon him, saw that he denounced him even more fervently than in the first case, and said hastily: أَقَتَلْتَ نَفْسًا زَكِيَّةً (Have you killed an innocent person?) meaning, a young person who had not yet committed any sin or done anything wrong, yet you killed him بِغَيْرِ نَفْسٍ (without Nafs) with no reason for killing him. لَّقَدْ جِئْتَ شَيْئًا نُّكْرًا (Verily, you have committed a thing Nukr!) meaning, something that is clearly evil. قَالَ أَلَمْ أَقُل لَّكَ إِنَّكَ لَن تَسْتَطِيعَ مَعِيَ صَبْرًا (He said: "Did I not tell you that you can have no patience with me?") Once again, Al-Khidr reiterates the condition set in the first place, so Musa says to him: إِن سَأَلْتُكَ عَن شَيْءٍ بَعْدَهَا (If I ask you anything after this,) meaning, 'if I object to anything else you do after this,' فَلَا تُصَاحِبْنِي ۖ قَدْ بَلَغْتَ مِن لَّدُنِّي عُذْرًا (keep me not in your company, you have received an excuse from me.) 'you have accepted my apology twice.' Ibn Jarir narrated from Ibn 'Abbas that Ubayy bin Ka'b said: "Whenever the Prophet ﷺ mentioned anyone, he would pray for himself first. One day he said: رَحْمَةُ اللهِ عَلَيْنَا وَعَلَى مُوسَى لَوْ لَبِثَ مَعَ صَاحِبِهِ لَأَبْصَرَ الْعَجَبَ، وَلَكِنَّهُ قَالَ: إِن سَأَلْتُكَ عَن شَيْءٍ بَعْدَهَا فَلَا تُصَاحِبْنِي ۖ قَدْ بَلَغْتَ مِن لَّدُنِّي عُذْرًا (May the mercy of Allah be upon us and upon Musa. If he had stayed with his companion he would have seen wonders, but he said, ('If I ask you anything after this, keep me not in your company, you have received an excuse from me.'))"