“Good actions give strength to ourselves, and inspire good actions in others.”

Saturnalia (c. 400). Alternately translated as "begot" instead of produced and "manners" instead of actions.

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 5.

Hays translation
V, 37
Meditations (c. AD 121–180), Book V

Light, Power and Wisdom (1959), p. 6; note that the short phrase "Be good, do good" had occurred in spiritual teachings of others in the 19th century, usually in conjunction with other injunctions. "Be Good, Do Good" became a prominent motto of the Divine Life Society.
Light, Power and Wisdom (1959), p. 207
Variant: Be good, do good, be kind, be compassionate.

Understanding Islam, "Morals and Ethics" http://vod.dmi.ae/media/96716/Ep_03_Morals_and_Ethics Dubai Media

Vol. I, p. 12
1980s, Letters to the Schools (1981, 1985)
Context: Goodness shows itself in behaviour and action and in relationship. Generally our daily behaviour is based on either the following of certain patterns — mechanical and therefore superficial — or according to very carefully thought-out motive, based on reward or punishment. So our behaviour, consciously or unconsciously, is calculated. This is not good behaviour. When one realizes this, not merely intellectually or by putting words together, then out of this total negation comes true behaviour.

"Reflections and Remarks on Human Life", VI: Right and Wrong, published in Works: Letters and Miscellanies of Robert Louis Stevenson -- Sketches, Criticisms, Etc. https://babel.hathitrust.org/cgi/pt?id=hvd.hwe7px (1895), p. 628.
Context: It is the mark of a good action that it appears inevitable in the retrospect. We should have been cut-throats to do otherwise. And there's an end. We ought to know distinctly that we are damned for what we do wrong; but when we have done right, we have only been gentlemen, after all. There is nothing to make a work about.