Full Idea
The best way to educate the younger generation (as well as yourself) is not to rebuke them but patently to practise all your life what you preach to others.
Gist of Idea
The best way to educate the young is not to rebuke them, but to set a good example
Source
Plato (The Laws [c.348 BCE], 729c)
Book Reference
Plato: 'The Laws', ed/tr. Saunders,Trevor J [Penguin 1970], p.193