What is the advice the Prophet Muhammad (saw) gave regarding those people who get a pledge of allegiance for worldly benefits?
 Narrated Abu Huraira:                     Allah's Apostle said, "There are three persons whom Allah will not look at on the Day of Resurrection, nor will he purify them and theirs shall be a severe punishment. They are: -1. A man possessed superfluous water, on a way and he withheld it from travelers. -2. A man who gave a pledge of allegiance to a ruler and he gave it only for worldly benefits. If the ruler gives him something he gets satisfied, and if the ruler withholds something from him, he gets dissatisfied. -3. And man displayed his goods for sale after the `Asr prayer and he said, 'By Allah, except Whom None has the right to be worshipped, I have been given so much for my goods,' and somebody believes him (and buys them). The Prophet then recited: "Verily! Those who purchase a little gain at the cost of Allah's Covenant and their oaths." (3.77)