Learn Texas Holdem

Question: My question is to whether a player who has already went all-in before the end of the hand and is waiting for the remaining players involved in the side pot to finish betting can flip over his cards.An example of this is that Player 1 has $20 Player 2 has $30 and Player 3 has $5. If at the beginning of the hand before the flop if player 3 goes all in and player 1 and 2 call. Because player 3 is now not involved in any betting action and is waiting for the betting to end can he reveal his cards.