Tafsir of Al-Anbiya' 21:9

ثم صدقناهم الوعد

Then We fulfilled to them the promise. the promise that their Lord made to destroy the evildoers. Allah fulfilled His promise and did that. He says:

فٲنجيناهم ومن نشاء

So We saved them and those whom We willed, meaning, their followers among the believers,

وأهلكنا المسرفين

but We destroyed Al-Musrifin. meaning, those who disbelieved the Message brought by the Messengers