Al-Burooj - 85:7

وَهُمْ عَلَى مَا يَفْعَلُونَ بِالْمُؤْمِنِينَ شُهُودٌ
[85:7]
And they were witnesses of what they did with the believers.
And they witnessed (all) that they were doing against the Believers.
And were themselves the witnesses of what they did to the believers.