In God we trust. All others must bring data.

W. Edwards Deming (1900-1993) American management consultant, educator

(Misattributed)

Variants: "All others must have/provide data."

Frequently attributed to Deming, probably through Mary Walton, The Deming Management Method, ch. 20 (1986), though it is presented there without attribution: "'In God we trust. All others must bring data.' If there is a credo for statisticians, it is that."

The earliest appearance in print comes from Edwin R. Fisher, Effect of Smoking on Nonsmokers: Hearing Before the Subcommittee on Tobacco of the Committee on Agriculture, House of Representatives, Ninety-fifth Congress, Second Session (7 Sep 1978): "I should like to close by citing a well-recognized cliche in scientific circles. The cliche is, 'In God we trust, others must provide data.'"

For more discussion see here.