This is a false quote which has been frequently paraphrased, wrongly attributed and / or taken out of context.
The idea of a 'big lie' is found in Mein Kampf where Hitler used to accuse the Jews of using this technique. This was then picked up by Goebbels who then applied it to the English, emphasizing the idea of repeating it. In 1941, Goebbels wrote:
The English follow the principle that when one lies, one should lie
big, and stick to it. They keep up their lies, even at the risk of
This appeared in an article he wrote titled Aus Churchills Lügenfabrik (Churchill's Lie Factory), the full text of which can be found here.
On the 'big lie', Goebbels is alleged to have said:
If you tell a lie big enough and keep repeating it, people will
eventually come to believe it. The lie can be maintained only for such
time as the State can shield the people from the political, economic
and or military consequences of the lie. It thus becomes vitally
important for the State to use all of its powers to repress dissent,
for the truth is the mortal enemy of the lie, and thus by extension,
the truth is the greatest enemy of the State.
This also appears to be a false quote, as this SE answer shows. The article False Nazi Quotations says that (in 2010), none of the internet sites or books using this quote gave a source.
The origin of the Hitler misquote may well be Walter Langer's 1943 OSS report A Psychological Analysis of Adolph Hitler where the author writes that one of Hitler's "primary rules" was
people will believe a big lie sooner than a little one; and if you
repeat it frequently enough people will sooner or later believe it.
Langer is not quoting Hitler here. He is simply providing an analysis based on the evidence available to him.