He who cheats (or deceives) does not belong to me!
Abu Hurairah (radiyallaahu-anhu) narrated that the Messenger of Allaah (sallal-laahu-alayhi-wasallam) passed by a pile of food and put his hand into it, and his fingers touched something wet. He said, ”What is this, O seller of the food?” The man said, ”It was (made wet) by the rain, O Messenger of Allaah.” He said, ”Why did you not put (the wet part) on top of the pile so that the people could see it? He who deceives does not belong to me.”
[Reported by Muslim: 102]