Abu Hurairah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings of Allah be upon him) said: "There are three people with whom Allah will not speak on the Day of Resurrection, nor will He purify them of their sins, and for them is a painful punishment: One is the person who pledged allegiance to an Imam, and if the Imam gave him (according to his desire), he fulfilled the pledge, but if he did not give him, he did not fulfill the pledge." __QUR_N__ Imam Tirmidhi says:
This hadith is Hasan Sahih and the ruling is unanimously in accordance with it.