When are you required to show cards

An issue came up last night that caused a bit of a heated discussion at the table. In a showdown situation "Player A" raised and was called. He immediately folded and mucked his cards. Two other players at the table demanded to see his cards saying if a player is called he has to show his cards. "Player A" contented that he can forfeit his hand at anytime, and that a player only has to show your cards if attempting to win the pot.

I wasnt involved in the hand but I am intersected in the answer. Unfortunately I have found conflicting info online.

Thanks

You have every right to see the those cards if you were in the hand or not doesn't matter as long as your at the table and in the game. You can ask see a losing call as well, this is good to do if you have a maniac calling station donkey, expose the donk and let the table see whats going on. Players can become upset by these techniques but it is part of the game.