GEN1094 If one is able, by word of mouth, to prevent harm befalling another, this also constitutes chesed.  An instance of this would be if, by chance, someone happened to meet a group of suspected robbers.  He believed that they intended to rob someone, since he overheard them discussing this person’s wealth.  It is his moral duty to misrepresent, to say that the intended victim is poor, even though he knows, in his heart, that this is not true ... So we find Abraham telling Sarah [this verse].  It would be even better if the person could forewarn the intended victim to guard himself against their nefarious designs.   He is certainly obliged to do so, according to the law of the Torah (end of the Chosen Mishpat).  AHAVCH 225