Amr bin Dinar عمرو بن دينار الأثرم الجمحي · Model Behavior of the Prophet (Kitab Al-Sunnah)

I went to Ubayy b. Ka’b and said him : I am confused about Divine decree, so tell me something by means of which Allah may remove the confusion from my mind. He replied : were Allah to punish everyone in the heavens and in the earth. He would do so without being unjust to them, and were he to show mercy to them his mercy would be much better than their actions merited. Were you to spend in support…

The boy whom al-Khidr had killed was created an infidel. Had he lived, he would have moved his parents to rebellion and unbelief.