Mukhtasar Muslim

It is narrated from Sayyiduna Abu Qatadah Ansari (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Avoid excessive swearing in trade, for it may promote the sale of goods but then erases (the blessing from it)."

Sayyiduna Abu Hurairah (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: There are three types of people with whom Allah will neither speak on the Day of Resurrection, nor will He look at them, nor will He purify them, and for them is a painful punishment. One is the person who keeps more water than he needs in the wilderness and withholds it from a traveler; the second is the person who sells something to someone after Asr prayer and swears that he bought it for such-and-such amount, and the buyer believes him, whereas he did not buy it for that amount (i.e., he swore falsely, and the mention of after Asr is because it is a blessed time when angels gather, or it is the original time for buying and selling); and the third is the person who pledges allegiance to the Imam for worldly gain. Then, if the Imam gives him some worldly goods, he fulfills his pledge, but if he does not give him, he does not fulfill it (so this person deceived the Muslims by pledging allegiance, and they relied on his promise, but he was only concerned with worldly gain and did not care about his pledge).