I beg the limitations here made may be remarked, when I say, that a miracle can never be proved, so as to be the foundation of a system of religion. For I own, that otherwise, there may possibly be miracles, or violations of the usual course of nature, of such a kind as to admit of proof from human testimony; though, perhaps, it will be impossible to find any such in all the records of history. Thus, suppose, all authors, in all languages, agree, that, from the first of January, 1600, there was a total darkness over the whole earth for eight days: suppose that the tradition of this extraordinary event is still strong and lively among the people: that all travellers, who return from foreign countries, bring us accounts of the same tradition, without the least variation or contradiction: it is evident, that our present philosophers, instead of doubting the fact, ought to receive it as certain, and ought to search for the causes whence it might be derived. The decay, corruption, and dissolution of nature, is an event rendered probable by so many analogies, that any phenomenon, which seems to have a tendency towards that catastrophe, comes within the reach of human testimony, if that testimony be very extensive and uniform.
ECHU, Section X, Part II. As has been noted plenty of times in the scholarly literature, this causes serious problems for those who think that Hume ever offers an in-principle or a priori (as opposed to merely empirical or a posteriori) argument against miracles; an in-principle argument should eliminate the days of darkness as well as (to use the very transparent example Hume uses) the resurrection of Elizabeth I. And Hume himself is quite explicit: the reason we should "form a general resolution" not to attend to any reports of religious miracles is the claim, which Hume thinks is discoverable from experience, that "the violations of truth are more common in the testimony concerning religious miracles, than in that concerning any other matter of fact". And thus Part I of the essay only serves to establish the standard that has to be met by any testimony of a 'violation of the usual course of nature'; the argument of the essay actually stands or falls not with that but with how accurate the observations in the beginning of Part II, about religious unreliability, are.
What is generally overlooked, but is quite clearly signaled by Hume at the very beginning of the essay, with the mention of Tillotson, and at the end of the essay, with the transparent talk about faith, is that Hume is turning popular anti-Catholic tropes and arguments, as used by Protestants, against Protestants as well. Protestant arguments about the gullibility of Catholics with regard to the miracles of the saints become Humean arguments about the gullibility of religious people generally with regard to miracles generally; Protestant arguments that we cannot rationally believe that transubstantiation occurs against the evidence of our senses find parallels in Hume's arguments against believing in religious miracles; and so forth. What is more, this seems not to have been lost on Hume's early critics; George Campbell, for instance, sees quite clearly what Hume is doing in (for instance) his long note on the Jansenist miracles, and, obviously, refuses to play the game, insisting that the parallels are artifical and based on false assumptions. In any case, these tropes were not typically in-principle arguments; they were based on claims about the mendacity of priests, the gullibility of poorly educated Catholics, and so forth.