Tafsir of Yunus 10:65

{And let not their speech grieve you} It is also recited as wa-lā yuḥzinuka (from aḥzanahu—to cause grief).

{Their speech} Meaning: their denial of you, their threats, their consultations regarding the planning of your destruction and the invalidation of your mission, and everything else they say concerning you.

{Indeed, all might belongs to Allah} This is a new sentence (isti’nāf) serving as a justification (ta’līl). It is as if it were asked: "Why should I not grieve?" So it was said: "Indeed, all might belongs to Allah." That is, all victory and subjugation in the kingdom belong entirely to Allah. No one possesses any part of it—neither they nor anyone else. Therefore, He will overcome them and grant you victory over them, as in: {Allah has written: "I will surely overcome, I and My messengers"} (Al-Mujadilah: 21), and {Indeed, We will support Our messengers} (Ghafir: 51).

Abu Ḥaywah recited it as anna al-‘izzah (with a fatḥah on the alif), meaning "because might belongs to Allah," making it an explicit justification. As for those who considered it a substitute (badal) for "their speech" and then rejected it, the rejection applies to their grammatical derivation, not to the recitation itself.

{He is the Hearing, the Knowing} He hears what they say, and He knows what they plot and resolve to do. He will requite them for that.

{Unquestionably, to Allah belongs whoever is in the heavens and whoever is on the earth. And those who invoke other than Allah do not follow [His] "partners." They follow not except assumption, and they are not but falsifying.}