Chapter 5, Part 4B - Lieh Tzu

So saying, Pien-ch'iao administered to each of them a potion of medicated wine, which threw them into a death-like trance lasting three days.

Then, making an incision in their breasts, he took out each man's heart and placed it in the other's body, poulticing the wounds with herbs of marvelous efficacy.

When the two men regained consciousness, they looked exactly the same as before; and, taking their leave, they returned home. Only it was Kung-hu who went to Ch'i-ying's house, where Ch'i-ying's wife and children naturally did not recognize him, while Ch'i-ying went to Kung-hu's house and was not recognized either.

This led to a lawsuit between the two families, and Pien-ch'iao was called in as arbitrator. On his explaining how the matter stood, peace was once more restored.
~ Lionel Giles translation via Terebess Asia Online ~

Go here to read the introductory post to the chapters of the Book of Lieh Tzu.