Simpler Rules: Rule 21

Rule 21: Cleaning Ball  

A ball on the putting green may be cleaned when lifted under Rule 16-1b. 

Elsewhere, a ball may be cleaned when lifted, except when such action is prohibited by another Rule or the ball has been lifted contrary to a Rule. If a player cleans a ball lifted in contravention of a Rule he incurs a penalty of one stroke in addition to any penalty applicable under that Rule.