As Allah commands, Hazrat Mahdi (pbuh) will never shed blood

http://www.mahdinevershedsblood.com/index.php

The command not to shed blood, is a command given to Hazrat Mahdi (pbuh) by our Prophet (may Allah bless him and grant him peace), it is a strict directive. As the necessity of this command of our Prophet (may Allah bless him and grant him peace) Hazrat Mahdi (pbuh) will never shed blood in any period of his life. Anyone who acts otherwise, that is anyone who sheds blood, in spite of the strict directive of our Prophet (saas) is definitely not the Mahdi (pbuh). 

People will seek refuge in the Mahdi (pbuh)as honey bees cluster around their sovereign. He will fill the world that was once full of cruelty, with justice. His justice will be as such that HE WILL NOT WAKE A SLEEPING PERSON NOT EVEN ONE DROP OF BLOOD IS SHED. The Earth will return to the age of happiness. (Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntazar, p. 29 and 48)

Hazrat Mahdi (pbuh)will follow the way of the Prophet (saas). HE WILL NOT WAKE UP A SLEEPING PERSON OR NO BLOOD WILL BE SHED. (Portents of Doomsday, p. 163)

IN THE TIME OF [HAZRAT MAHDI (pbuh)] NO ONE WILL BE WOKEN UP FROM THEIR SLEEP OR HAVE A BLEEDING NOSE. (Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntazar, p. 44)

Those who swear allegiance to him [Hazrat Mahdi (pbuh)] will swear allegiance between the Corner and the Maqam [near the Kaaba]. THEY WILL NOT WAKEN THE SLEEPER, AND THEY WILL NEVER SHED BLOOD. (Al-Haythami, Al-Qawl al-Mukhtasar, p. 24)

War (competents) will lay down its burden (arms and the like). (Sunan Ibn Majah, 10/334)

War (competents)  put down their weighs [their weapons, etc.]. (Imam Sharani, Death-Doomsday-Hereafter and The Signs of the End Times, p. 496)

Enmity and hatred between people will cease… Like the cup fills with water, so will earth fill with peace... There will be religious unity. Nobody but Allah will be worshipped. War will put down its burden. (Sunan Ibn Majah, 10/334)

There will be no enmity left between any people. And all hostility, fighting, and envy will definitely disappear. (Imam Sharani, Death-Doomsday-Hereafter and The Signs of the End Times, p. 496)