The destitute you shall not favor in his complaint (Exodus 23:3)
There are many ways that those who have are commanded to help those who have not. Those with means have to leave portions of their fields for the poor. We have to lend to the poor. A certain tithe was designated for the poor. We are obligated to help them in other ways as well. But there’s one arena in which we may not give the needy extra consideration: in court. Court is a place of justice, not of mercy. If a poor person were to steal from a rich person (for example), we would not be permitted to justify the crime. The judges must decide cases fairly, based on the facts. They may not favor the poor out of pity and, as we shall see in Mitzvah #234, they may also not favor the rich and powerful in order to honor them.
The reason for this mitzvah is clear: it would mean a complete breakdown of the legal system if judges were permitted to disregard the facts of a case and render decisions based on their personal emotions.
This mitzvah applies in all times and places to the members of a beis din. In the Talmud, it can be found in the tractate of Chulin (134a). In the Shulchan Aruch, it is codified in Choshen Mishpat 17. It is #277 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #66 of the 194 negative mitzvos that can be fulfilled today as listed in the Chofetz Chaim’s Sefer HaMitzvos HaKatzar.