وَهُمْ عَلَىٰ مَا يَفْعَلُونَ بِٱلْمُؤْمِنِينَ شُهُودٌ
Saheeh International(7) And they, to what they were doing against the believers, were witnesses. [1896]
English Translation - Rowwad Translation Centerand were witnessing what they did to the believers[2].
English Translation - Hilali and Khan7. And they witnessed what they were doing against the believers (i.e. burning them).