وَهُمْ عَلَىٰ مَا يَفْعَلُونَ بِٱلْمُؤْمِنِينَ شُهُودٌۭ
Sentence structure
هُمْ is the topic and شُهُودٌ its predicate. عَلَىٰ مَا يَفْعَلُونَ is linked to the predicate; يَفْعَلُونَ is the relative clause of مَا with an omitted returning object.
Ayah summary
They watched the believers burn in the fire and showed them no mercy.
وَهُمْ — And they
Grammar: وَ coordinates, while هُمْ is a detached third-person masculine-plural pronoun functioning as the topic.
عَلَىٰ — over
Grammar: A preposition governing the following relative pronoun and linked to شُهُودٌ.
مَا — what
Grammar: A relative pronoun in the genitive position after عَلَىٰ; its relative clause follows.
يَفْعَلُونَ — they were doing
Grammar: A third-person masculine-plural indicative imperfect forming the relative clause. Attached و is the subject, final ن marks the indicative, and the returning object is omitted.
بِٱلْمُؤْمِنِينَ — to the believers
Grammar: بِ is a preposition, ٱل the definite article, and مُؤْمِنِينَ a masculine-plural active participle in the genitive, marked by yāʾ.
شُهُودٌۭ — witnesses
Grammar: An indefinite masculine-plural nominative active participle functioning as the predicate of هُمْ.