The Gateless Gate, by Ekai, called Mu-mon, tr. Nyogen Senzaki and Paul Reps [1934], at sacred-texts.com
Daibai asked Baso: "What is Buddha?"
Baso said: "This mind is Buddha."
Mumon's comment: If anyone wholly understands this, he is wearing Buddha's clothing, he is eating Buddha's food, he is speaking Buddha's words, he is behaving as Buddha, he is Buddha. This anecdote, however, has given many a pupil the sickness of formality. If one truly understands, he will wash out his mouth for three days after saying the word Buddha, and he will close his ears and flee after hearing "This mind is Buddha."