Do not seek to be a ruler
Narrated `Abdur-Rahman bin Samura:The Prophet (may the peace and blessings of Allah be upon him) said, "O `Abdur-Rahman! Do not seek to be a ruler, for if you are given authority on your demand then you will be held responsible for it(Allah will not help you), but if you are given it without asking (for it), then you will be helped (by Allah) in it. If you ever take an oath to do something and later on you find that something else is better, then you should expiate your oath and do what is better."
"Do not seek to be a ruler" ie: do not ask it for yourself, do not wish it, do not expect it, do not aspire to get it one day; it is a trust which the weak can not bear or fulfill its rights, even if the leader exerted his efforts to establish the justice, he must commit mistakes for which he will be asked on the day of Resurrection. It is often an affliction, not a grant as many people assume.
Seeking to be a ruler is not completely forbidden, it is disliked unless the seeker is incompetent to it, or it is more likely that he can not perform it fully, or he seeking it so as to attain a personal worldly benefit then it would be prohibited.
There is no doubt that seeking the ruler ship causes people to suspect the seeker and mistrust him. The Prophet (may the peace and blessings of Allah be upon him) did not ever authorize to be a ruler anyone who sought it.