Here is a link to a translation of one of Hakuin's writings, as mentioned by Anders.Keiso Dokuzui
It's a brief commentary on Tozan's Five Ranks, relating them to actualization of the Four Wisdoms/Three Bodies. It describes Zen's gate which is the recognition of one's own Dharmakaya wisdom (kensho/Great Perfect Mirror Wisdom), the subsequent actualization of Sambhogakaya (i.e. embodiment/integration through practice of the Jewel Mirror Samadhi, which is fulfillment of the Universal Nature Wisdom), and finally Nirmanakaya as the free functioning within activity (fulfillment of the Marvelous Observing Wisdom and Perfecting-of-Action Wisdom).
A quote from the Sixth Patriarch in that text sums all of this up: "The pure Dharmakaya is your nature; the perfect Sambhogakaya is your wisdom; the myriad Nirmanakayas are your activities".