Whence do I derive (the same for) the first-born of Cham and Cush? (viz. Genesis 10:6) From (Psalms 78:51) "And He struck every first-born in Egypt, the first fruit of their strength in the tents of Cham."
God Struck Even the Firstborn of Ham and Cush Living in Egypt
Mekhilta Tractate Pischa 7:8