Laws of Cricket 1947 Code - Law 44
The Fieldsman may stop the ball with any part of his person, but if he wilfully stop it otherwise five runs shall be added to the run or runs already made; if no run has been made five shall be scored. The penalty shall be added to the score of the Striker if the ball has been struck, but otherwise to the score of Byes, Leg Byes, No Balls or Wides as the case may be.
Notes on Law 44
1. A fieldsman must not use his cap, etc., for the purpose of fielding a ball.
2. The five runs are a penalty and the batsmen do not change ends.
Reproduction of the Laws of Cricket is by kind permission of Marylebone Cricket Club