The Holy Prophet [s] said: "He who sleeps bearing deceit against his Muslim brother in his heart, has slept in the wrath of Allah and remains in that case until he repents."
Safinat-ul-Bihar, vol. 2, p. 318
The Holy Prophet [s] said: " ...And he who deceives his Muslim brother, Allah takes away the abundancy of his sustenance and spoils his livelihood and leaves him to his ownself."
Wasa'il-ush Shi'ah, vol. 17, p. 283
Imam Sadiq [a] said: "The Holy Prophet [s] prohibited that milk be mixed with water for sale."
At-Tahthib, vol. 7, p. 13
Imam Sadiq [a] said: "Those who play imposture with us (Muslims in general) is not from us."
The Holy Prophet [s] said: "The person who deceives a Muslim believer in buying or selling (things), is not of us, and, on the Resurrection Day, will be raised among the Jews, because they have been the most deceitful against Muslims."
Bihar-ul-Anwar, vol. 103, p. 80