Chofetz Chaim Daily 10 Taamuz 3:7 One must judge his fellow favorably as it says Bitzedek tishpot amisecha. Often, not doing so leads to LH (see sefer for more details). 3:8 Even in scenario that one isnt obligated to judge favorably, one still must not relate what he saw, unless all the conditions are met. See chapters 4, 5, & 10.
Chofetz Chaim Daily 11 Taamuz 4:1 Asur to degrade someone about his parents’ negative actions or his own past misdeeds. Asur to tell about someone actively doing something wrong bein adam l’Makom. 4:2 Even a slight wrongdoing is asur to report i.e. not keeping a minhag etc.