Musnad Ahmad 3240

It was narrated that Yazeed bin Hurmuz said: Najdah wrote to Ibn ‘Abbas (رضي الله عنه), asking him about killing children. He wrote to him (saying): You wrote to me and asked about killing children. The Messenger of Allah (ﷺ) did not kill them, and you should not kill them, unless you know about them what the companion of Moosa knew about the boy.