“Righteousness is the root of happiness.”

The Dalai Lama at Harvard: Lectures on the Buddhist Path to Peace (1988) by Jeffrey Hopkins.
Context: What is the Great Vehicle? What is the mode of procedure of the Bodhisattva path? We begin with the topic of the altruistic intention to achieve enlightenment in which one values others more than oneself. The Great Vehicle path requires the vast motivation of a Bodhisattva, who, not seeking just his or her welfare, takes on the burden of bringing about the welfare of all sentient beings. When a person generate this attitude, they enter within the Great Vehicle, and as long as it has not been generated, one cannot be counted among those of the Great Vehicle. This attitude really has great power; it, of course, is helpful for people practicing religion, but it also is helpful for those who are just concerned with the affairs of this lifetime. The root of happiness is altruism — the wish to be of service to others.

§ 182
Source: Pali Canon, Sutta Pitaka, Khuddaka Nikaya (Minor Collection), (Suttas falling down)

Source: Natural Right and History (1953), p. 6

"Sunisa Lee Says She's 'Going to Delete Twitter' So She Can Focus on Preparing for Beam Final" in People (1 August 2021) https://people.com/sports/tokyo-olympics-sunisa-lee-going-to-delete-twitter-focus-preparing-beam-final/

"The Farmer", Tinker, Tailor (1922).

This is from a letter written to Washington on 9 October 1789 by the synod of the Reformed Dutch Church of North America (image of the letter on the Library of Congress site here http://memory.loc.gov/mss/mgw/mgw2/038/0650049.jpg). Washington quoted the portion in bold in his reply.
Misattributed

The Story of the Flower.