Here is Dogen, from one of his lectures (as recorded by Koun Ejo):
Is the way attained through mind or body? In the teaching schools it is said that since body and mind are not separate, the Way is attained through the body. Yet it is not clear that we attain the Way through the body, because they say ‘since’ body and mind are not separate. In Zen the Way is attained through both body and mind.
As long as we only think about the buddha-dharma with our minds we will never grasp the Way, even in a thousand lifetimes or a myriad of eons. When we let go of our minds and cast aside our views and understandings the Way will be actualized. One sage clarified True Mind (Reality) when he saw peach blossoms and another realized the Way when he heard the sound of tile hitting a bamboo. They attained the Way through their bodies. Therefore, when we completely cast aside our thoughts and views and practice shikantaza, we will become intimate with the Way. For this reason the Way is doubtlessly attained through the body. That is why I encourage you to practice zazen wholeheartedly.
(Dogen, “Shobogenzo zuimonki: Sayings of Eihei Dogen Zenji recorded by Koun Ejo”, tr. Shohaku Okumura, Sotoshu Shumucho pg 107-108)
Here’s Shunryu Suzuki, from a lecture he gave at Tassajara:
If you are not disturbed by the sound of the bluejay when you are reading something, the bluejay will come right into your heart, and you will be a bluejay, and the bluejay will be reading something.
(from the video, Shunryu Suzuki Discusses the Sandokai: Sound and Noise)
Like Dogen’s “sound of tile hitting a bamboo”, Suzuki’s “sound of the bluejay” illustrates how the Way is realized, but Suzuki’s example also shows how the sound becomes action.
If I were to try to explain Suzuki’s example, I would say that the sound of the bluejay shifts the location of awareness relative to the center of gravity, and the movement of breath that incorporates the shift reads the book.
Dogen asserts that the clarification of True Mind at the sight of peach blossoms was attained through the body. The key to the clarification of True Mind (“heart-mind”) is again the shift in the location of awareness relative to the center of gravity, and the movement of breath that incorporates the shift in action.
Sitting shikantaza is the place itself, and things. … People who are moving around outside all sit with you. They don’t take the sitting posture!
(Aspects of Sitting Meditation: “Shikantaza”)
If I am undisturbed by the presence of things within the range of my senses (the bluejay), and also undisturbed by the presence of things beyond the range of my senses (“people moving around outside”), the things enter into my heart, I become the things, and the things sit the posture.