Musannaf Ibn Abi Shayba 23:128

Ibn Numayr narrated to us, he said: Muhammad ibn Abi Isma'il narrated to us, from Ma'qil al-Khath'ami, who said: A man came to Ali while he was in the Rahba and said: "O Commander of the Faithful, what is your opinion regarding a woman who does not pray?" He said: "Whoever does not pray is a disbeliever."