Im in trouble if I didnt know how to stop all of it! guys please help me, iwould appreiciate it!

so theres a friend of mine lets call him P, he pranked me and said that a guy in our school which is a total stranger to him but a close friend of Mine got slapped in the cinema and everyone started laughing at him.
now my close friend is really pissed about it and he is planning to do something really bad to P, because it wasnt true, and I dont want that to happen since P was just fooling around!! so I need a really good lie or something that can calm my friend down!! please!

Don't lie to your friend! Simply tell him he can get into trouble and the re think his actions. Also, explain that P was just messing around.