Rule 27: Ball lost or out of bounds; Provisional ball.

(b) When provisional ball becomes ball in play.
The player may play a provisional ball until he reaches the place where the original ball is likely to be. If he makes a stroke with the provisional ball from the place where the original ball is likely to be or from a point nearer the hole than that place, the original ball is lost and the provisional ball becomes the ball in play under penalty of stroke and distance. If the original ball is lost outside a water hazard or is out of bounds, the provisional ball becomes the ball in play, under penalty of stroke and distance. If there is reasonable evidence that the original ball is lost in a water hazard, the player must proceed in accordance with rule 26-1.
(c) When provisional ball is to be abandoned.
 If the original ball is neither lost nor out of bounds, the player must abandon the provisional ball and continue playing the original ball. If he makes any further strokes at the provisional ball, he is playing a wrong ball and the provisions of rule 15 apply. Note: If a player plays a provisional ball under rule 27-2a, the strokes made after this rule has been invoked with a provisional ball abandoned under rule 27-2c and penalty strokes incurred solely by playing that ball are disregarded.