3:154

Then after sorrow He sent down security upon you, a calm coming upon a party of you, and (there was) another party whom their own souls had rendered anxious; they entertained about Allah thoughts of ignorance quite unjustly, saying: We have no hand in the affair. Say: Surely the affair is wholly (in the hands) of Allah. They conceal within their souls what they would not reveal to you. They say: Had we any hand in the affair, we would not have been slain here. Say: Had you remained in your houses, those for whom slaughter was ordained would certainly have gone forth to the places where they would be slain, and that Allah might test what was in your breasts and that He might purge what was in your hearts; and Allah has knowledge of the secrets of your hearts.
Meaning:-
Slay: kill, murder, put to death.
Purge: to rid of whatever is impure or undesirable; cleanse; purify.