And when Musa said to his people: Call to mind Allah's favor to you when He delivered you from Firon's people, who subjected you to severe torment, and slew your sons and spared your women; and in this there was a great trial from your Lord.

So Allah protected him from the evil (consequences) of what they planned, and the most evil punishment overtook Firon's people:

Say to those of the dwellers of the desert who were left behind: You shall soon be invited (to fight) against a people possessing mighty prowess; you will fight against them until they submit; then if you obey, Allah will grant you a good reward; and if you turn back as you turned back before, He will punish you with a painful punishment.

Allah has prepared for them severe chastisement, therefore be careful of (your duty to) Allah, O men of understanding who believe! Allah has indeed revealed to you a reminder,