Source, in full
Attributed in Wisdom for the Soul : Five Millennia of Prescriptions for Spiritual Healing (2006) by Larry Chang, p. 352; this statement appears in late 20th century inspirational books, but with no known citation to original material by Tolstoy.
Notes from Wikiquote
This is an aphorism penned by Kozma Prutkov, a fictional author invented by the Count Aleksey Tolstoy (a distant relative of Leo Tolstoy's) and the Zhemchuzhnikov brothers (from "Thoughts and Aphorisms", first published in the weekly "Iskra", 1860).