What is the ruling on praying behind a person who has been seen in a position violating Islamic morals, and is it permissible to pray behind him if he repents?

What this person did by looking at the woman and enabling her to touch his body and private parts is forbidden, based on Allah's saying: "Tell the believing men to reduce [some] of their vision and guard their private parts" and the Prophet's (peace be upon him) saying: "For one of you to be stabbed in the head with an iron needle is better for him than to touch a woman he is not lawful to." And massage by a strange woman is even more forbidden than mere touch. Praying behind him is permissible if he repents. If you do not know his state, then assume his repentance. If he continues his action, then it is preferable to pray behind someone else, but praying behind him is valid like with other transgressors.