Fantalaqaa hattaa izaa laqiyaa ghulaaman faqatalahoo qaala aqatalta nafsan zakiy yatam bighairi nafs; laqad ji'ta shai'an nukraa
So they set out, until when they met a boy, he [i.e., al-Khidhr] killed him. [Moses] said, "Have you killed a pure soul for other than [having killed] a soul? You have certainly done a deplorable thing."
1 Mufti Taqi Usmani
So, they moved ahead until when they met a boy, he killed him (the boy). He (Mūsā) said, “Did you kill an innocent soul while he did not kill anyone? You have committed a heinous act indeed.”