Musannaf Ibn Abi Shayba 28:600

33128. Abd al-Rahim ibn Sulayman narrated to us, from Muhammad ibn Ishaq, from al-Zuhri and Muhammad ibn Ali, from Yazid ibn Hurmuz, who said: Najdah wrote to Ibn Abbas asking him about the killing of children, and he said in his letter: "The scholar, the companion of Musa, killed the young boy." Yazid said: I wrote the letter of Ibn Abbas with my own hand to Najdah: "You wrote asking about the killing of children, and you say in your letter that the scholar, the companion of Musa, killed the young boy. If you knew about the children what that scholar knew about that young boy, you would have killed them. But you do not know. The Messenger of Allah (may Allah bless him and grant him peace) has forbidden their killing, so refrain from them."