Musar for Chullin 177:4

And there is stealing that is not considered stealing by the laws of people, but is considered stealing by the laws of heaven, such as one who decides in one's mind to enter in judgment with one's friend in order to collect money from the friend without doing violence, just because one's eyes deceived him, and one brings monetary damage to the friend, even without a fight or misuse, just by the simple emotion, having clean hands, and even if from the decision the friend would be forced to pay all, the spirit of the Place does not abide with him, and does this as a tax owed by the friend, one transgresses "love your neighbor as yourself" which is a general rule in the Torah, and it is in instances like this that they said "a person is known by their pocket" (Eruvin 65b). And according to the basic material, stealing is forbidden and the teshuvah is difficult, behold it says "one who steals even a cent from one's friend is likened to one who stole the soul from the friend, and the soul from the friend's sons and daughters" (Bava Kamma 119a) and while the stolen money is in one's hands there is no possible atonement, and it is very difficult to return food that was stolen (Chulin 99a). And behold a person who fears Hashem will be cautious and will guard oneself very much from anything that is forbidden in any aspect it can exist, and will deal all one's business faithfully, and even when a good opportunity appears, and those who sell are being stricken with harsh punishments, one will never extend one's hands towards stealing God forbid, because it is better for a person to die of starvation than to become an evildoer even for an hour in the Place's eyes, and "those who seek Hashem do not lack what is good" (Ps. 34:11) because God does not withhold good to those who walk in simple ways.