BALL LOST OR OUT OF BOUNDS Provisional Ball Rule 27 ( From R&A quick guide to the rules)
If your ball is lost (outside a water hazard) or is out of bounds you must play another ball from the spot where the last shot was played, under penalty of one stroke, i.e. stroke and distance.
You are allowed 5 minutes to search for a ball. If it is not found within 5 minutes, it is lost.
If, after playing a shot, you think your ball may be lost (outside a water hazard) or out of bounds you should play a provisional ball. You must state that it is a provisional ball and play it before you go forward to search for the original ball.
If the original ball is lost (other than in a water hazard) or is out of bounds, you must continue with the provisional ball, under penalty of one stroke. If the original ball is found in bounds, you must continue play of the hole with it, and must stop playing the provisional ball.
A player does not have to search for their ball if it is not visible and they choose not to play it. However, if someone finds a ball that is believed to be the player’s original ball before they have played their provisional ball from a point nearer to the hole than where it is thought that the original ball may be, then the player must identify it and if it is their original ball must continue play with it. In stroke play, it is considered good etiquette for a fellow competitor NOT to search for a ball that the player wishes to abandon, but in match play an opponent may choose to search for it if they consider that it is to their advantage to find it.”