Wellspring

The words of a man's mouth are as deep waters, and the wellspring of wisdom as a flowing brook.

Source: tatoeba (5486969)

We’re so often taught to simply believe in ourselves—to trust our instincts—that to see a narrative in which second-guessing oneself and refusing one’s deepest impulses is a potential wellspring of charity and good is, in itself, noteworthy.

Source: wiktionary

Krapp’s Last Tape has been acted by prisoners in San Quentin and made into a chamber opera. It goes to the wellspring of an actor. Well, most of the time: when Albert Finney played the part, Beckett went to sleep in rehearsals.

Source: wiktionary