Abu Hurairah (May Allah be pleased with him) said:

The Messenger of Allah (ﷺ) said, "He who takes up arms against us is none of us; and he who cheats us is none of us." <b>[Muslim]</b>. Another narration of Muslim is: The Messenger of Allah (ﷺ) happened to pass by a heap of corn. He thrust his hand in that (heap) and his fingers felt wetness. He said to the owner of that heap of corn, "What is this?" He replied: "O Messenger of Allah! These have been drenched by rainfall." He remarked, "Why did you not place this (the drenched part of the heap) over the corn so that people might see it? He who deceives is not of us."

وعن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏"‏ من حمل علينا السلاح، فليس منا، ومن غشنا، فليس منا‏"‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏ وفي رواية له أن رسول الله صلى الله عليه وسلم مر على صبرة طعام، فأدخل يده فيها، فنالت أصابعه بللا، فقال‏:‏ ‏"‏ ما هذا ياصاحب الطعام‏؟‏‏"‏ قال أصابته السماء يارسول الله، قال‏:‏ ‏"‏ أفلا جعلته فوق الطعام حتى يراه الناس‏!‏ من غشنا فليس منا‏"‏‏.‏