Musannaf Ibn Abi Shayba 38:157

Humaid narrated to us, from al-Hasan, from his father, who said: I bear witness that the letter of Umar ibn Abd al-Aziz was read to us. In it, he stated: "If they shed forbidden blood and cut off the path (highway robbery), then [you must fight them]." He disavowed the Haruriyyah in his letter and ordered that they be fought.