pawn promotion

here is one event which is happen in one tournament about pawn promotion

the player pushes his piece to eith(8) d8 rank with out changing its shape.but later after he pushed to the eith rank he changed it to queen.his opponent opposes his action by saying alraedy you placed it with out promoting so it continues as piece.the judge also decided as the later player.the question is is there fide or other rule which says if a pawn is reached the eith rank with out promoting ,then it continues as pawn.

please explain for me briefly if you can with examples

I'm quite sure that once a pawn reaches the 8th/1st rank it must promote.  The player doesn't have a choice to leave it as a pawn.