so you did not slay them but in fact allah slew them and o dear prophet you did not throw when you did throw but in fact allah threw and in order to bestow an excellent reward upon the muslims indeed allah is the all hearing the all knowing.
فلم تقتلوهم ولكن الله قتلهم وما رميت إذ رميت ولكن الله رمى وليبلي المؤمنين منه بلاء حسنا إن الله سميع عليم