Musar su Salmi 7:9

Another insight to be aware of, and which I believe to be correct, is that when our teacher Moshe killed the Egyptian it seems to have been the beginning of Egypt’s downfall and from that time forth their guardian angel seems to have been on the wane. For the Ari writes (Likkutei Torah, 55a; Sha’ar HaPesukim, 26a) that Moshe killed the Egyptian with the Divine Name Y-CH-SH [יכ"ש], which is one of the components of the forty-two part Name. This name derives from the verse, “Who appointed you to be an officer or judge?” — Miy samcha le’ish sar veshofeit (Shemos 2:14). For this Name had the power to subdue the Egyptians and to wreak vengeance upon them. King Dovid alludes to it in the verse, “Judge me, Hashem, according to my righteousness” — Shafteini Y-H-V-H ketzidki (Tehillim 7:9), the acronym of which also spells out this Name.