Sforno on Exodus 9:20/ספורנו על שמות ט׳:כ׳

1הירא את דבר ה' הניס, G’d continues explaining to Moses that the reason He had told Moses to advise the Egyptians to bring their cattle under cover was that he knew that anyone genuinely afraid of G’d’s warnings would avail himself of this warning and save himself and his herds.