When a thief recites a blessing, he angers God (Psalms 10:3).
The Talmud explains this verse as referring to someone who stole wheat, ground it into flour, and kneaded it into dough, then took off the required tithe for the Kohen (priest) and recited the blessing for the tithe. Far from being pleased with this prayer, God becomes angry, for not only did this person sin by stealing, but he or she had the audacity to pronounce God's Name over something acquired dishonestly (Bava Kama 94a).
Much of Torah law deals with business. Indeed, the greatest piety is achieved when people observe the laws regulating commercial transactions and property rights, and thereby respect other's belongings and rights (Bava Kama 30a). Doing a mitzvah with something not acquired honestly is the grossest of all distortions.
In a highly competitive society, we may think that all is fair, especially if we can find a way to make dishonest actions appear legitimate. The Torah condemns such thinking."