From Job 14:19. Used in common speech as an idiom, conveying the proverb wherein just as water can wear down a stone over time, with persistence and perseverance a person can achieve unthinkable goals. Apparently, this is also a Buddhist proverb (or maybe it just gets quoted as such because its "cooler" to quote Buddhist proverbs than biblical ones).
There is a lovely story about Rabbi Akiva concerning this idiom. As the story goes (according to Avot de-Rabbi Natan), at the age of 40 Akiva wasn't a scholar yet, but a shepherd (isn't it weird how everybody in Jewish tradition starts out as a shepherd), and didn't even know how to read and write. One day he came to the well and asked, "who carved this stone here?". "The water that drips on it so frequently every day", the people at the well said to him, "haven't you read in the scripture that the waters wear the stones?" Akiva judged himself very harshly for not being familiar with the verse and especially in relation to itself, "for if the soft sculpted the hard, then the words of the scripture, as hard as iron, how much more so should carve my heart of flesh and blood". And then he went with his son to a beginner's teacher, who tought them Aleph and Beth and so on. And he studied until he knew all of the scripture. Then he went to Rabbi Eliezer and Rabbi Joshua and asked them to teach him the secondary sources, and they gave him one piece of law to study. And he sat and argued with himself, "why was this Aleph written", "why was this Beth written" and so on for every letter. Then he came back to the Rabbis and discussed his questions with them, and Rabbi Tarfon said to him, "For you it was written (Job 28:11) He searches the sources of the rivers and brings hidden things to light. The things that are hidden to men, Rabbi Akiva brings to light". Rabbi Akiva went on to revolutionize Jewish scholarship, essentially founding the branch of Rabbinical Judaism (as opposed to Messianic or Karaite Judaism).
In Hebrew, the corresponding text is "אבנים שחקו מים". If you know Hebrew you will find the phrase amusing, because a naive reading of it will translate as "stones wore waters".
You see, Hebrew is very lax when it comes to the order of words in a sentence. Where English mostly uses word order to distinguish the grammatical roles of words and clauses, Hebrew mostly uses different articles for different cases. So for example, the house in the nominative case will be הבית (ha-bayit), but in the objective case will be את הבית (et ha-bayit). This allows the speaker to jumble up the word order of a sentence and still retain the meaning -- very useful when writing poetry! Still, people usually stick to the traditional order of "<subject> <verb> <object>" to construct their sentences (especially for such simple sentences as "waters wore stones"), unless you want to emphasize some part by bringing it to the front of the sentence.
Job apparently wanted to emphasize the stones: so effective is the water that it wears stones. The problem is that there is no difference in article between an indefinite noun in the nominative and an indefinite noun in the objective (the Hebrew version of the text has both stones and waters as indefinite), so the sentence now reads naively "stones wore waters". Of course, that reading doesn't make sense so we revert to the inverted one. But isn't that the point of the phrase to begin with?: that incredibly while stones are "harder" than waters, the waters still wear the stones over time. Well, if we are supposed to think of the stones really as "harder", why is it that the simple reading of the phrase, "stones wore waters", must be rejected in favor of a convoluted one? I've always found this amusing.