Tafsir of Sad 38:81

That which He has ordained and appointed for the annihilation of the creatures, which is the time of the first Trumpet blast, not the time of the Resurrection, which is the one being inquired about.

The particle fa (in "fa-innahu") is not for connecting the act of granting respite to the request for respite, but rather for connecting the information to that which is emphasized by it, as in His, the Almighty’s, saying: "If he steals, a brother of his has stolen before him," and the saying of al-Shafi’i:

"If You show mercy, then You are worthy of that."