Surah Al-Kahf — Ayah 74 (18:74)
فَٱنطَلَقَا حَتَّىٰٓ إِذَا لَقِيَا غُلَٰمٗا فَقَتَلَهُۥ قَالَ أَقَتَلۡتَ نَفۡسٗا زَكِيَّةَۢ بِغَيۡرِ نَفۡسٖ لَّقَدۡ جِئۡتَ شَيۡـٔٗا نُّكۡرٗا ٧٤
English translation (Saheeh International)
So they set out, until when they met a boy, he [i.e., al-Khiḍr] killed him. [Moses] said, "Have you killed a pure soul for other than [having killed] a soul? You have certainly done a deplorable thing."
Brief commentary
After they disembarked from the ship they set out walking along the seashore, when they saw a young boy who was still not an adult playing with the other boys. Khidr killed him and Moses said to him: Did you kill a pure soul that is still a minor for no sin? You have really done something evil!!