Musnad Ahmad 30:324

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Three [types of people] Allah will not speak to, nor will He look at them, nor will He purify them, and they shall have a painful punishment: A man who has surplus water in the wilderness and withholds it from the wayfarer; and a man who pledges allegiance to an Imam, not pledging it except for the sake of worldly gain—if he gives him from it, he fulfills it for him, and if he does not give him, he does not fulfill it for him." He said: "And a man who sells a commodity to a man after the afternoon prayer (Asr), then swears to him by Allah that he took it for such-and-such a price, and he (the buyer) believes him, while he is upon other than that."