Albert Einstein was on his way to becoming a household name when he took a trip to Japan in 1922. The scientist had just learned that he would be awarded the Nobel Prize in Physics, and word of his accomplishments was spreading beyond his home country of Germany. In light of his rising stardom, he gave an unconventional tip to his bellboy after checking into his Tokyo hotel: He jotted down a note on a piece of paper in place of giving him cash, saying it "will probably be worth more than a regular tip" in the future. Nearly a century later, NBC News reports, the same note has sold at auction for $1.3 million.

The message, which has come to be referred to as “Einstein’s Theory of Happiness,” looks much different from the ideas about time and space the theoretical physicist is known for. It reads: "A calm and modest life brings more happiness than the pursuit of success combined with constant restlessness.”

Menahem Kahana, Getty Images

On Tuesday, October 24, the item went to auction in Jerusalem along with a second note reading "Where there's a will there's a way" that Einstein wrote for the bellboy on the same occasion. The first message was scribbled on official Imperial Hotel paper and the second on a blank sheet of scrap paper. Both were signed and dated 1922.

Following a 25-minute bidding war, Einstein’s theory of happiness was claimed by an anonymous buyer for $1.3 million, making it the highest-priced document ever sold at auction in Israel. The second artifact sold for more than $200,000, according to the auction house. It may have taken a while to pay off, but Einstein's gift turned out to be one of the most generous tips in history. Whether it's going to a relative or descendent of the bellboy is unclear; both seller and buyer are unidentified.   

The Hebrew University in Jerusalem, which Einstein helped found, was bequeathed his literary estate and personal papers upon his death. Earlier this year, letters on God, Israel, and physics brought in $210,000 at an auction in the Israeli capital.

[h/t NBC News]