The gates of Zen

To see form but not be corrupted by form or to hear sound but not to be corrupted by sound is liberation. Eyes that aren't attached to form are the gates of Zen. In short, those who perceive the existence and nature of phenomena and remain unattached are liberated. Those who perceive the external appearance of phenomena are at their mercy. Not to be subject to afflictions is what's meant by liberation. There's no other liberation. When you know how to look at form, form doesn't give rise to mind and mind doesn't give rise to form. Form and mind are both pure. ~ Bodhidharma' s Wake-up Sermon

Source:
www.purifymind.com/Sutras19.htm