Known sourcecanonical
"Of right and wrong he taught Truths as refined as ever Athens heard; And (strange to tell!) he practised what he preached."
John Armstrong / The Art of Preserving Health. Book iv. Line 301.
The Art of Preserving Health. Book iv. Line 301.
Bartlett's Familiar Quotations, 9th ed. (Little, Brown, 1905), public domain