“Happiness exists on earth, and it is won through prudent exercise of reason, knowledge of the harmony of the universe, and constant practice of generosity.”

Source: The Doctrine of the Mean

Ibid., p. 328
The Book of Disquiet
Original: Não há felicidade senão com conhecimento. Mas o conhecimento da felicidade é infeliz; porque conhecer-se feliz é conhecer-se passando pela felicidade, e tendo, logo já, que deixá-la atrás. Saber é matar, na felicidade como em tudo. Não saber, porém, é não existir.

"On the Harmony of Theory and Practice in Mechanics" (Jan. 3, 1856)

"Morality and Birth Control", February-March, 1918, pp. 11,14.
Birth Control Review, 1918-32

St. 1.
A Song for St. Cecilia's Day http://www.englishverse.com/poems/a_song_for_st_cecilias_day_1687 (1687)
Context: From harmony, from heavenly harmony,
This universal frame began:
When nature underneath a heap
Of jarring atoms lay,
And could not heave her head,
The tuneful voice was heard from high,
'Arise, ye more than dead!'
Then cold, and hot, and moist, and dry,
In order to their stations leap,
And Music's power obey.
From harmony, from heavenly harmony,
This universal frame began:
From harmony to harmony
Through all the compass of the notes it ran,
The diapason closing full in Man.

Source: Sufi Thought and Action

Source: The Bhagavadgītā (1973), p. 169–70. (12.)

Concluding Paragraph
On Practice (1937)
Original: (zh-CN) 通过实践而发现真理，又通过实践而证实真理和发展真理。从感性认识而能动地发展到理性认识，又从理性认识而能动地指导革命实践，改造主观世界和客观世界。实践、认识、再实践、再认识，这种形式，循环往复以至无穷，而实践和认识之每一循环的内容，都比较地进到了高一级的程度。这就是辩证唯物论的全部认识论，这就是辩证唯物论的知行统一观。