“Invention, strictly speaking, is little more than a new combination of those images which have been previously gathered and deposited in the memory: nothing can come of nothing.”

Source: Haroun and the Sea of Stories

Introduction
A Treatise of Human Nature (1739-40)
Context: Nothing is more usual and more natural for those, who pretend to discover anything new to the world in philosophy and the sciences, than to insinuate the praises of their own systems, by decrying all those, which have been advanced before them. And indeed were they content with lamenting that ignorance, which we still lie under in the most important questions, that can come before the tribunal of human reason, there are few, who have an acquaintance with the sciences, that would not readily agree with them. 'Tis easy for one of judgment and learning, to perceive the weak foundation even of those systems, which have obtained the greatest credit, and have carried their pretensions highest to accurate and profound reasoning. Principles taken upon trust, consequences lamely deduced from them, want of coherence in the parts, and of evidence in the whole, these are every where to be met with in the systems of the most eminent philosophers, and seem to have drawn disgrace upon philosophy itself.

Source: Meditations (c. 121–180 AD), Book IV, 4

Richter II p. 126 no. 837 books.google http://books.google.de/books?id=A7dUhbBfmzMC&pg=PA126
The Notebooks of Leonardo da Vinci (1883), I Prolegomena and General Introduction to the Book on Painting

The Ultimate Quotable Einstein by Alice Calaprice lists this as "probably not by Einstein". However, this post from quoteinvestigator.com http://quoteinvestigator.com/2014/04/29/common-sense/ traces it to a reasonably plausible source: the second part of a three-part series by Lincoln Barrett (former editor of 'Life' magazine) titled "The Universe and Dr. Einstein" in Harper's Magazine, from May 1948, in which Barrett wrote "But as Einstein has pointed out, common sense is actually nothing more than a deposit of prejudices laid down in the mind prior to the age of eighteen." Since he didn't put the statement in quotes it could be a paraphrase, and "as Einstein has pointed out" makes it unclear whether Einstein said this personally to Barrett or Barrett was recalling a quote of Einstein's he'd seen elsewhere. In any case, the interview was republished in a book of the same title, and Einstein wrote a foreword which praised Barrett's work on the book, so it's likely he read the quote about common sense and at least had no objection to it, whether or not he recalled making the specific comment.
Unsourced variant: Common sense is the collection of prejudices acquired by age eighteen.
Disputed

Source: True and False: Heresy and Common Sense for the Actor

Variant: Happiness is nothing more than good health and a bad memory.

Source: The Natural and Artificial Right of Property Contrasted (1832), p. 14