مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3240
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
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.
Musnad Ahmad 3264Its isnad is saheeh, Muslim (1812)]