c. 180 · Irenaeus of Lyons, Against Heresies 4.15.2
And not only so, but the Lord also showed that certain precepts were enacted for them by Moses, on account of their hardness [of heart], and because of their unwillingness to be obedient, when, on their saying to Him, “Why then did Moses command to give a writing of divorcement, and to send away a wife?” He said to them, “Because of the hardness of your hearts he permitted these things to you; but from the beginning it was not so;” thus exculpating Moses as a faithful servant, but acknowledging one God, who from the beginning made male and female, and reproving them as hard-hearted and disobedient. And therefore it was that they received from Moses this law of divorcement, adapted to their hard nature.