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."