In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. A wise man, therefore, proportions his belief to the evidence. […] No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavors to establish.

David Hume (1711-1776) Scottish philosopher, economist, historian, empiricist
An Enquiry Concerning Human Understanding, Sec. 10 “Of Miracles,” Part 1 (1748)

Often given as just, "A wise man proportions his belief to the evidence."