Musnad Ahmad 5:395

Bahz narrated to us, Hammam narrated to us, Qatadah informed us, from Abu Hassan, that Ali used to command a matter, and it would be brought to him, and it would be said: "We have done such and such." He would say: "Allah and His Messenger have spoken the truth." Al-Ashtar said to him: "This which you say has spread among the people. Is it something the Messenger of Allah, peace and blessings of Allah be upon him, entrusted to you specifically?" Ali said: "The Messenger of Allah, peace and blessings of Allah be upon him, did not entrust anything to me specifically, excluding the people, except for something I heard from him, which is in a scroll in the sheath of my sword." He said: They did not cease [asking] him until he brought out the scroll. He said: And in it was: "Whoever introduces an innovation, or harbors an innovator, upon him is the curse of Allah, the angels, and all the people. Neither a mandatory nor a voluntary deed will be accepted from him." He said: And in it was: "Indeed, Ibrahim declared Makkah sacred, and I declare Madinah sacred; all that is between its two lava fields and its protected land is sacred. Its vegetation is not to be cut, its game is not to be startled, its lost property is not to be picked up except by one who announces it, no tree is to be cut from it except for a man to feed his camel, and weapons are not to be carried in it for fighting." He said: And in it was: "The blood of the believers is equal, the lowest of them strives for their protection, and they are a united hand against those who are other than them. Beware, a believer is not to be killed for a disbeliever, nor is one who has a covenant to be killed while in his covenant."