“Mind is Buddha” is the phrase for one who wants medicine while he has no disease. “No Mind, No Buddha” is given to those who have been cured of disease but still cling to medicine.
A monk asked Baso, “Why do you teach that Mind is Buddha?”
Baso replied, “To stop a baby's crying.”
The monk asked, “ What is it like when the baby stops crying?”
Baso answered, “No Mind, no Buddha.”
In connection with “Mind is Buddha,” there is an interesting story in Nanbanji Kohai-ki (History of Nanbanji):
In the 16th century, a great religious debate was held at Nanbanji between Buddhists and a Portugese Catholic Father who was much favored by Oda Nobunaga, an influential feudal lord of that time. The Portugese Priest was a man of wide erudition and was familiar with the Buddhist Sutras. Representatives of various Buddhist schools were all debated down by his eloquence. Finally Zen Master In of Nanzenji in Kyoto, was selected as the last debater.
The Portugese Priest asked, “What is Buddha?”
“Mind is Buddha” answered Master In.
The Portugese Father now unsheathed a dagger, thrust it at Master In's chest, and demanded “What is 'Mind is Buddha'?”
Master In, not perturbed in the least, shouted: “KWATZ!”
The Portugese Priest fell into a swoon in spite of himself and the audience
including Lord Nobunaga, all paled.
— from Zenkei Shibayama,
Zen Comments on the Mumonkan (1974), p. 225