Musar su Salmi 119:121

The fourth of Yitro's requirements, that they be שונאי בצע, abhor unjust gain, refers to a quality such as demonstrated by David who is described as performing "justice and charity simultaneously." (Samuel II 8,15) It says there: ויהי דוד עושה משפט וצדקה, and the Talmud in Sanhedrin 6 on that verse explains that David first handed down a verdict based on justice. When he found the convicted party too poor to pay the judgment he would pay the judgment out of his own pocket. The reason he did so was that he was afraid that he might have erred and then the convicted litigant would certainly not be able to walk away happy from Court, as we had stated earlier that he should. Midrash Shemuel, commenting on Psalms 119,121, in which David is reported as having prayed: “עשיתי משפט וצדקה, אל תניחני לעושק," "I have performed justice and charity, do not hand me over to the oppressor," explains that David prayed that his charitable nature should not be taken advantage of by those wicked ones who knew him.