Rules cover that:
3.7 e
"When a player, having the move, plays a pawn to the rank furthest from its starting position, he must exchange that pawn as part of the same move for a new queen, rook, bishop or knight of the same colour on the intended square of arrival."
3.10 b
"A move is illegal when it fails to meet the relevant requirements of Articles 3.1 – 3.9 "
So, that move would be illegal and if called by the opponent, the appropriate penalty would apply.
Article 7.5 covers illegal moves.
Edit: For some reason this was posted twice. Link to other post here: https://www.chess.com/forum/view/general/pawn-promotion-irregularity-1?page=1#last_comment