Musannaf Ibn Abi Shayba 28:210

'Abd al-Rahim ibn Sulayman narrated to us, from 'Abd al-Malik ibn Sa'id ibn Hayyan, from 'Ammar al-Duhni, who said: Abu al-Tufayl narrated to me, saying: I was in the army that 'Ali ibn Abi Talib sent to the Banu Najiyah. We reached them and found them in three groups. Our commander said to one group among them: "Who are you?" They said: "We are a people who were Christians and we accepted Islam, and we remained steadfast upon our Islam." He said: "Withdraw." Then he said to the second: "Who are you?" They said: "We are a people from the Christians; we did not see a religion better than our religion, so we remained steadfast upon it." He said: "Withdraw." Then he said to another group: "Who are you?" They said: "We are a people who were Christians and we accepted Islam, then we reverted, and we did not see a religion better than our religion, so we became Christians." He said to them: "Accept Islam," but they refused. He said to his companions: "When I wipe my head three times, then attack them." They did so, and they killed them and took the offspring captive. I brought the offspring to 'Ali, and Masqalah ibn Hubayrah came and bought them for two hundred thousand. He brought one hundred thousand to 'Ali, but he refused to accept it. Masqalah went away with his dirhams, and Masqalah went to them and freed them, then he joined Mu'awiyah. It was said to 'Ali: "Will you not take the offspring?" He said: "No," and he did not interfere with them.