Musannaf Ibn Abi Shayba 37:544

Humaid ibn Abd al-Rahman narrated to us, from Muhammad ibn Muslim, from Ibrahim ibn Maysara, who said: I said to Tawus, "Is Umar ibn Abd al-Aziz the Mahdi?" He said, "He was indeed guided (mahdi), but he is not him (the Mahdi). For the Mahdi, when he is, will increase the doer of good in his good, and will accept repentance from the doer of evil for his evil." "He will distribute wealth, be severe upon the workers (officials), and show mercy to the poor."