وَمَكْرَ ٱلسَّيِّئِ وَلَا يَحِيقُ ٱلْمَكْرُ ٱلسَّيِّئُ إِلَّا بِأَهْلِهِۦ فَهَلْ يَنظُرُونَ إِلَّا سُنَّتَ ٱلْأَوَّلِينَ فَلَن تَجِدَ لِسُنَّتِ ٱللَّهِ تَبْدِيلًا
"An evil scheme closes in upon none but its own author. Are they waiting for anything but the way of those who went before? You will find no change in God's way."
يَحِيقُ — root ح-ي-ق: that a thing should turn back and close in upon its owner. The root was treated in Ghāfir (al-Muʾmin) at 40/45 and in al-Zumar at 39/48. I do not repeat it here.
The way the sentence is built is worth recording: lā yaḥīqu … illā bi-ahlih — negation + exception. That is, the possibility of the evil scheme's going somewhere else is closed off.
سُنَّتَ ٱللَّه — the root س-ن-ن was analysed in detail in al-Fatḥ at 48/23 (to open a way, to make flow; sinān, masnūn). I do not repeat it here.
And in Ghāfir (al-Muʾmin) at 40/85 the close of that sūra was made with this word: sunnata'llāhi'llatī qad khalat fī ʿibādih. The two sūras use the same concept for the same work: continuance.
فَلَن تَجِدَ لِسُنَّتِ ٱللَّهِ تَبْدِيلًا — and the unchangeability is declared with the particle lan (absolute negation).