Allah will inspire Hazrat Mahdi (as) with the truest law

... Hazrat Mahdi (as) WILL RULE WITH THE LAW OF THE PROPHET DAVID (AS) and will seek no witness or evidence from anyone. Shaykh al-Mufid says: "WHEN HAZRAT MAHDI (AS) APPEARS HE WILL RULE WITH THE SAME SECRET KNOWLEDGE AS THE PROPHET DAVID (AS), and will rule with no need for witnesses. (Shaykh al-Mufid, Kitab al-Irshad, pp. 365-366)

IN HIS [HAZRAT MAHDI’S (AS)] TIME NO EVIL WILL BE DONE TO ANYONE. (Al-Mahdi al-Maw'ud, Vol. 1, pp. 280, 300)