Musannaf Ibn Abi Shayba 3:5192

Waki’ narrated to us, Sufyan narrated to us, from Ibrahim ibn Abi Hafsa, who said: I said to Ali ibn al-Husayn: "Indeed, Abu Hamza al-Thumali—and there was extremism in him—says: 'We do not pray behind the Imams, and we do not intermarry except with those who hold the same view as we hold.'" Ali ibn al-Husayn said: "Nay, we pray behind them, and we intermarry with them according to the Sunnah."