ALL BUDDHA-TATHAGATAS TOGETHER have been simply transmitting wondrous dharma and actualizing anuttara samjak sambodhi [supreme perfect enlightenment] for which there is an unsurpassable, unfabricated, wondrous method. This wondrous dharma, which has been transmitted only from buddha to buddha without deviation, has as its criterion jijuyu zanmai. For disporting oneself freely in this samadhi, practicing zazen in an upright posture is the true gate. Although this dharma is abundantly inherent in each person, it is not manifested without practice, it is not attained without realization.
From: Talk on the Wholehearted Practice of the Way -
Kosho Uchiyama (with Shohaku Okumura, Taigen Daniel Leighton)
When the buddha-tathagatas each having received the one-to-one transmission of the splendid Dharma, experience the supreme state of bodhi, they possess a subtle method that is supreme and without intention. The reason this [method] is transmitted only from buddha to buddha, without deviation, is that the samadhi of receiving and using the self is its standard. For enjoyment of this samadhi the practice of [Za]zen in the erect sitting posture, has been established as the authentic gate. This Dharma is abundantly present in each human being, but if we do not practice it, it does not manifest itself, and if we do not experience it, it cannot be realized. From: Bendowa - A Talk about Pursuing the Truth - Nishijima-Cross