Imam Muhammad Baqir (a.s.) says that one day the Messenger of Allah (S) was passing through the market. He saw a grain seller selling food grains (wheat or barley). He said it was of a good quality. But revelation descended on him and he put his hand deep inside the sack and drew out grain of low quality. The man had topped the sack with high quality grain to fool the customers. The Holy Prophet (S) was angry and he said,
“You have done Khayanat with Muslims and practiced adulteration.”7
He (S) also said,
“One who resorts to adulteration in his dealings with Muslims is not a Muslim. He shall be raised with the Jews on the day of Judgement. Because the Jews are the most common adulterators with Muslims.”8
The Prophet of Allah (S) says that one who sleeps with the intention of practicing adulteration with his brother (the next day), sleeps with the displeasure of Allah (S.w.T.). He begins his day while Allah (S.w.T.) is angry with him. Allah (S.w.T.) continues to be wrathful with him till he does not repent and give up adulteration. If he dies without repenting he dies a death of a non-Muslim. After this he (S) said thrice,
“Know that! One who adulterates with Muslims is not of Muslim. And Allah removes barakat from the sustenance of one who adulterates with his Muslim brother. Allah stops his sustenance and leaves him to Himself.9
Imam Ja’far as-Sadiq (a.s.) told a flour seller to keep aloof from adulteration because one who practiced adulteration will himself be a victim of adulteration. If he has no wealth to be adulterated there will be adulteration with his family.(Wasa’il ul-Shia Vol. 12 page 210)