The 251st prohibition is that we are forbidden from verbally wronging another person by telling him things that will distress and humiliate him, and make him discouraged.1 For example, when a person has sinned in his youth, but changed his ways, and someone tells him, "Thank G‑d who has taken you away from that path to this good path," or similar indirect references to faults that cause him pain.

The source of this prohibition is G‑d's statement2 (exalted be He), "V'lo sonu one another and you shall fear your G‑d." Our Sages3 said that this refers to verbally causing him pain (ona'as devarim).4

In the words of the Sifra, "The verse 'V'lo sonu one another' refers to ona'as devarim. What does this mean? If the person is a baal teshuvah, do not tell him, 'Remember your previous deeds...'; if there was illness...[do not say as Job's friends did, 'has anyone perished who was totally innocent?']; if you see donkey drivers...[who are seeking grain to buy, do not say that they can obtain it by a certain person, who in reality has nothing to sell and the drivers will be disappointed]; do not ask, 'how much does this cost?' [when you don't intend to make a purchase, since it will cause disappointment to the seller]."

Our Sages said,5 "Ona'as devarim is more serious than ona'as mamon, since regarding the former, the Torah says, 'and you shall fear your G‑d.'"6

The details of this mitzvah are explained in the 4th chapter of tractate Bava Metzia.