Then (fear) Allah, in your own self; for, by Allah, you are not being shown anything as if you are blind or being apprised of anything as if you are ignorant. The ways are clear while the banners of faith are fixed. You should know that among the creatures of Allah, the most distinguished person before Allah is the just Imam who has been guided (by Allah) and guides others. So, he stands by the recognised ways of the Prophet's behaviour and destroys unrecognised innovations. 
The (Prophet's) ways are clear and they have signs, while innovations are also clear and they too have signs. Certainly, the worst man before Allah is the oppressive Imam who has gone astray and through whom others go astray. He destroys the the accepted sunnah and revives abandoned innovations. I heard the Messenger of Allah saying: "On the Day of Judgement the oppressive Imam will be brought without anyone to support him or anyone to advance excuses on his behalf, and then he will be thrown into Hell where he will rotate as the hand-mill rotates, then (eventually) he will be confined to its hollow."
I swear to you by Allah that you should not be that Imam of the people who will be killed because it has been said that, "An Imam of this people will be killed after which killing and fighting will be made open for them till the Day of Judgement, and he will confuse their matters and spread troubles over them. As a result, they will not discern truth from wrong. They will oscillate like waves and would be utterly misled." You should not behave as the carrying beast for Marwan so that he may drag you wherever he likes, despite (your) seniority of age and length of life.
(1) Al-Baladhuri, Ansab, V, 60;
(2) al-Tabari, Ta'rikh, V, 96, events of 34 H.;
(4) al-Mufid, al-Jamal, 100;
(5) Ibn Miskawayh, Tajarib al-'umam (1909), I, 478.