Gratian, Concordia discordantium canonum,  Tractatus de legibus (ca. 1130 Dictum before chapter 1,

  Humanum genus duobus regitur, naturali uidelicet iure et moribus. Ius naturae est, quod in lege et euangelio continetur, quo quisque iubetur alii facere, quod sibi uult fieri, et prohibetur alii inferre, quod sibi nolit fieri. Unde Christus in euangelio: "Omnia quecunque uultis ut faciant uobis homines, et uos eadem facite illis. Haec est enim lex et prophetae. [Matthew 7:12, cf. Luke 6:31]" (The Human Race is ruled by two things:  namely, natural ius and  mos.  The ius of nature is what is contained in the lex and the Gospel.  By it, each person is commanded to do to others what he wants done to himself and is prohibited from inflicting on others what he does not want done to himself. This is the lex and the prophets.)

K÷ln, Erzbisch÷fliche Di÷zesan- und Dombibliothek , fol. 9ra