Rashi on Exodus 4:8/רש"י על שמות ד׳:ח׳

1והאמינו לקל האת האחרון THEY WILL BELIEVE THE VOICE OF THE LATTER SIGN — As soon as you say to them, “On your account have I been smitten — because I uttered slander about you”, they will believe you, for they are already experienced in this: that those who combine to harm them are smitten by plagues, e. g., Pharaoh and Abimelech who were punished on Sarah’s account.