Musnad Ahmad 3176

It was narrated that Yazeed bin Hurmuz said: Najdah bin ‘Amir wrote to Ibn ‘Abbas (رضي الله عنه) asking him about some things. I saw Ibn ‘Abbas (رضي الله عنه) when he read his letter and when he wrote his reply. He wrote to him (saying): You asked me... And he narrated the hadeeth. And he said: You asked me, did the Messenger of Allah (ﷺ) kill any of the boys of the mushrikeen? The Messenger of Allah (ﷺ) did not kill any of them and you should not kill any of them unless you know about them what al-Khadir know about the boy when he killed him.