The story
The proverb is a paraphrase of a similar proverb from the biblical Book of Job (14:19), or perhaps a translation of that proverb: אֲבָנִ֤ים ׀ שָׁ֥חֲקוּ מַ֗יִם avanim, shahaqu mayim; literally: rocks - have been graded down (by) water, which has been translated: Water wears away stones, or in the King James version, (because the word mayim for water is seemingly in the plural, ending with -yim ): "The waters wear the stones".
Etymology from Wiktionary, CC BY-SA 4.0.