A dharma teaching by Huihai (8th century, disciple of Mazu):
[A sutra says:] Wise men regulate their minds rather than their persons; fools regulate their persons rather than their minds. Another sutra states: ‘Evil springs forth from the mind, and by the mind is evil overcome.’ Thus, we may know that all good and evil proceed from our minds and that mind is therefore the root.
Q: By what means is the root-practice to be performed?
A: Only by sitting in meditation, for it is accomplished by dhyana (ch’an) and samadhi.
Q: Please describe dhyana and samadhi.
A: When wrong thinking ceases, that is dhyana; when you sit contemplating your original nature, that is samadhi, for indeed that original nature is your eternal mind.
Blofeld, John: Zen teaching of instantaneous awakening;
being the teaching of the Zen master Hui Hai.
Devon 2015, p. 44-45