Pay it forward

is asking the beneficiary of a good deed to repay it to others instead of to the original benefactor.

 The concept is old, but the phrase may have been coined by Lily Hardy Hammond: "You don't pay love back; you pay it forward.", in her 1916 book In the Garden of Delight.

"In the order of nature we cannot render benefits to those from whom we receive them, or only seldom. But the benefit we receive must be rendered again, line for line, deed for deed, cent for cent, to somebody."- Ralph Waldo Emerson, in his 1841 essay Compensation.

I do not pretend to give such a deed; I only lend it to you. When you [...] meet with another honest Man in similar Distress, you must pay me by lending this Sum to him; enjoining him to discharge the Debt by a like operation, when he shall be able, and shall meet with another opportunity. I hope it may thus go thro' many hands, before it meets with a Knave that will stop its Progress. This is a trick of mine for doing a deal of good with a little money. Benjamin Franklin, in a letter to Benjamin Webb dated April 25, 1784

 "You can't pay anyone back for what has happened to you, so you try to find someone you can pay forward." AA anonymous spokesman.

Ray Bradbury advised that writers he has helped thank him by helping other writers.