The Buddha (Siddhārtha Gautama) was the north Indian teacher whose discourses, preserved in the Pāli Canon, include the ‘Book of the Threes’ passage this quote paraphrases. He taught that his Dhamma was open to all — “shining in the open, not under cover” — the opposite of a secret, initiate-only doctrine. The catchier ‘sun, moon and truth’ rewording is the later work of the Tamil Buddhist scholar P. Lakshmi Narasu, whose 1907 book compressed the discourse into a single memorable line.