Wrong ball

You must not make a stroke at a wrong ball. In match play: If you make a stroke at a wrong ball, you get the general penalty (loss of hole).

If you and your opponent play each other’s ball during the play of a hole, the first to make a stroke at a wrong ball gets the general penalty (loss of hole).
But if it is not known which wrong ball was played first, there is no penalty and the hole must be played out with the balls exchanged.

In stroke play: If you make a stroke at a wrong ball, you get the general penalty (two penalty strokes) and must correct the mistake by continuing play with the original ball by playing it as it lies or taking relief under the Rules:

The stroke made with the wrong ball and any more strokes before the mistake is corrected do not count.
If you do not correct the mistake before making a stroke to begin another hole or, for the final hole of the round, before returning your scorecard, you are disqualified.

Related Rule - 6.3c