The steady drip of water causes stone to hollow and yield.
Stilicidi casus lapidem cavat.
Original text (Latin)
Notes from Wikiquote
Compare: "The soft droppes of rain pierce the hard marble; many strokes overthrow the tallest oaks", John Lyly, Euphues, 1579 (Arber's reprint), p. 81
Variants
Continual dropping wears away a stone.