For a truth, once established by proof, does neither gain force nor certainty by the consent of all scholars, nor lose by the general dissent.

Maimonides (1135-1204) Spanish Jewish philosopher, scholar, astronomer, physician [Moses ben Maimon, Rambam, רמב״ם]

Guide for the Perplexed, Part 2, ch. 15 (c. 1190) [tr. Friedlander (1885)]
    (Source)

Alternate translation:

For when something has been demonstrated, the correctness of the matter is not increased and certainty regarding it is not strengthened by the consensus of all men of knowledge with regard to it. Nor could its correctness be diminished and certainty regarding it be weakened even if all the people on earth disagreed with it.
[tr. Pines (1963)]