What is the ruling on someone who ate an onion, then forgot and went to pray in congregation, then noticed a bad smell during the prayer? Should he cut short his prayer? And can Allah afflict a person with things that hinder him from worship, despite his repentance and desire for obedience, to see the extent of his good presumption of Allah?

It is disliked for someone who has eaten garlic, onions, or anything with an offensive odor to attend congregational prayer in the mosque before removing the smell, so as not to cause discomfort to the worshippers. If he attends in this state, he has done wrong, and he should leave before the prayer to remove the odor. However, if he has already entered into an obligatory prayer, he is not permitted to cut it short, because invalidating an obligatory prayer after commencing it is forbidden, due to His Almighty's saying: "And do not invalidate your deeds." Nevertheless, Shafi'i jurists have explicitly stated the permissibility of breaking off from the imam and completing the prayer quickly to prevent harm to the worshippers and to attain the reward of congregational prayer. So, if he fears causing harm to people, it is permissible for him to break off from the imam and complete his prayer individually if there is a benefit in doing so.