Al-Khadir slew a young man

AL-KAHF (THE CAVE) : 74-76

18:74. Then they proceeded: until, when they met a young man, he slew him. Moses said: "Hast thou slain an innocent person who had slain none? Truly a foul (unheard of) thing hast thou done!"
18:75. He answered: "Did I not tell thee that thou canst have no patience with me?"

18:76. (Moses) said: "If ever I ask thee about anything after this, keep me not in thy company: then wouldst thou have received (full) excuse from my side."