(Hakuin's own explanation, as translated by Phillip Yampolksy in The Zen Master Hakuin: Selected Writings, pg. 164 --the painting at left is by Hakuin himself)
And from another source:
'Zen grannies', shrewd old women who love to confound pompous monks, are a frequent occurrence in Zen literature, and Hakuin had run-ins with a few himself. "Old San", one such lady, couldn't wait to test Hakuin when he visited her home town. In the interview, Hakuin held up one hand, silently challenging her to hear its sound. She yelled, "Better than listening to Hakuni's 'one hand', let's clap both and do some real business!" Hakuin shot back, "If you can do business by clapping both hands, then there's no need to hear the sound of one", and he grabbed a piece of paper and brushed a painting of a bamboo broom on it. He passed it to Old San for an inscription. She wrote:This broomThis confrontation itself has become a koan: "Who won? Hakuin or Old San?".
All the imposters in Japan--
First of all
Hakuin of Hara!
(from John Stevens Three Zen Masters: Ikkyu, Hakuin, Ryokan pp. 83-84 [BQ9298 .S72 1993])