The Gateless Gate, by Ekai, called Mu-mon, tr. Nyogen Senzaki and Paul Reps [1934], at sacred-texts.com
33. This Mind Is Not Buddha
A monk asked Baso: "What is Buddha?"
Baso said: "This mind is not Buddha."
Mumon's comment: If anyone understands this, he is a graduate of Zen.
If you meet a fencing-master on the road, you may give him your sword, If you meet a poet, you may offer him your poem. When you meet others, say only a part of what you intend. Never give the whole thing at once.