penny saved is a penny earned, a

A penny spar'd is twice got.
[1640 G. Herbert Outlandish Proverbs no. 506]

By the same proportion that a penny saved is a penny gained, the preserver of books is a Mate for the Compiler of them.
[a 1661 T. Fuller Worthies (Hunts.) 51]

This I did to prevent expences, for‥a penny sav'd, is a penny got.
[1695 E. Ravenscroft Canterbury Guests ii. iv.]

I saved five pounds out of the brickmaker's affair. ‥It's a very good thing to save one, let me tell you: a penny saved, is a penny got!
[1853 Dickens Bleak House ix.]

I can save money this way; and believe me, laddie, nowadays‥a penny saved is a penny earned.
[1923 Wodehouse Inimitable Jeeves xi.]

‘A penny saved is a penny earned, but what can I buy with it?’
[2001 Washington Post 6 Dec. C11 (Family Circus comic strip)]

Related to: thrift

Bibliography of major proverb collections and works cited from modern editions is available here.

What one does not spend, one will have. This maxim for thrift is so familiar that it often appears in shortened form, as in Although they can afford to buy a house right now, they're putting it off, on the principle of "a penny saved." It appeared in slightly different form in George Herbert's Outlandish Proverbs (1640). Whether or not it originally suggested that savings earn interest is not known.