Musannaf Ibn Abi Shayba 37:534

Waki’ narrated to us, from Fudayl ibn Marzuq, who heard it from Maysarah ibn Habib, from al-Minhal, from Sa’id ibn Jubayr, from Ibn Abbas, who said: "From us are three: from us is al-Saffah, from us is al-Mansur, and from us is al-Mahdi."