But when erring reason proposes something as being commanded by God, then to scorn the dictate of reason is to scorn the commandment of God.

Thomas Aquinas (1225-1274) Italian friar, philosopher, theologian

Summa Theologica 1a-2ae, q. 19, art. 5, ad 2 (1265-1274)
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Often quoted without the first clause, which changes the meaning. Alt. trans.: "To disparage the dictate of reason is equivalent to contemning the command of God."