وَدَخَلَ ٱلْمَدِينَةَ عَلَىٰ حِينِ غَفْلَةٍ مِّنْ أَهْلِهَا فَوَجَدَ فِيهَا رَجُلَيْنِ يَقْتَتِلَانِ … فَوَكَزَهُۥ مُوسَىٰ فَقَضَىٰ عَلَيْهِ قَالَ هَٰذَا مِنْ عَمَلِ ٱلشَّيْطَٰنِ … قَالَ رَبِّ إِنِّى ظَلَمْتُ نَفْسِى فَٱغْفِرْ لِى
"He entered the city at a moment when its people were unaware and found two men there fighting… Moses struck him with his fist and finished him. 'This is of Satan's doing,' he said… 'My Lord! I have wronged myself; forgive me,' he said."
The event is told without its outcome being hidden, and Moses' own assessment of it is transmitted as well: hādhā min ʿamali'sh-shayṭān, innī ẓalamtu nafsī.
I record this as an observation: the text does not cover over a grave event in the life of a prophet, and it has the assessment made by him. And the character of the event is named in the verse: not a deliberate killing but the unlooked-for result of an intervention. Wakaza — to strike with the fist; fa-qaḍā ʿalayh — he finished him.
And the meeting with the same man on the following day is worth recording (18-19): the one who asks for help is once again in a fight. What Moses says to him stands in the text: innaka la-ghawiyyun mubīn — "you are plainly one gone astray."
I record this as my own reading, and its ground is the order of the verses: the story shows that the one who stands on the side of the wronged does not pass untested either. That is, being "made weak" does not of itself bring rightness of conduct — and this is a note set beside the promise in the fifth verse of the sūra.
وَجَآءَ رَجُلٌ مِّنْ أَقْصَا ٱلْمَدِينَةِ يَسْعَىٰ (20) — "and a man came running from the far end of the city."
The same pattern occurs in Yāsīn at 36/20 as well (wa jāʾa min aqṣa'l-madīnati rajulun yasʿā). In both places someone who is not named comes running and brings word of something. This is an overlap that can be verified from the text.