Musannaf Ibn Abi Shayba 19:931

Abu Bakr narrated to us, he said: Abd al-Rahim ibn Sulayman narrated to us, from Abd al-Rahman ibn Ubayd, from his father, who said: There were people who used to take the stipend and the provision and pray with the people, while they were worshipping idols in secret. Ali ibn Abi Talib brought them and placed them in the mosque—or he said: in the prison—then he said: "O people, what is your opinion regarding a people who used to take the stipend and the provision and worship these idols?" The people said: "Kill them." He said: "No, but I will do to them as was done to our father Abraham, may the blessings of Allah be upon him." So he burned them with fire.