In my thesis I want to use the following quotation in the epigraph of a chapter:
It is very difficult to predict — especially the future.
There are many variations of this quote, and the authorship is attributed to many different people. Very often it is assigned to Niels Bohr, and one of the oldest secondary sources I have found dates back to 1971.
How should I cite this secondary quotation in my epigraph?
Something like the following? —Niels Bohr (Mencher, 1971)