I don't recall the refernce to Clarke's Third Law explicitly, but he actually used the substance of it.
... the Anacreonian civilisation is basically taken over by Salvor Hardin's new religion of science.
Interestingly, this wasn't the original intention of the Foundation citizens (though it was of course part of Seldon's 1,000 year plan). They simply created the religion as the most convenient way to spread atomic technology to the Four Kingdoms who have regressed into barbarism (The Galactic Spirit Did It). It's only later that they realized that they now hold power over the people of these kingdoms, if not the rulers.
In addition, a book in Foundation sequel series - but NOT Asimov's book - used the reverse of the Law's wording:
Any technology that does not appear magical is insufficiently advanced.
Gregory Benford, in Foundation's Fear (1997)