Verse 17

فَلَمْ تَقْتُلُوهُمْ وَلَـٰكِنَّ ٱللَّهَ قَتَلَهُمْ وَمَا رَمَيْتَ إِذْ رَمَيْتَ وَلَـٰكِنَّ ٱللَّهَ رَمَىٰ وَلِيُبْلِىَ ٱلْمُؤْمِنِينَ مِنْهُ بَلَآءً حَسَنًا إِنَّ ٱللَّهَ سَمِيعٌ عَلِيمٌ

Therefore, you did not kill them; on the contrary, God had already damned them. And you did not throw, when you threw, it was God who threw. And this is in order to test the faithful with the best of tests. Indeed God is All Hearing All Knowing.