Some times people of different faith give us very hard time. Similar thing happened to one shaikh and he challenged them that to come and sit on one side and he would make dua to God that the liar be killed in 3 days. I heard that kuffar ran away. Is such a thing allowed? I know Rasool Allah PBUH at one point took ahle bayt and the nasara ran away?
This is called the Mubahala. The Messenger of Allah (pbuh) did this; but this was amongst his specialties. We, the regular people of this ummat, should not do this because there are no tangible results that are guaranteed by this action.
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