Athanasius of Alexandria

Thus fathers often call their sons their servants, yet without denying the genuineness of their nature. In fact, they often affectionately call their own servants children, yet without losing sight of the fact they did purchase them originally. For they use the one appellation from their authority as fathers, but in the other they speak from affection. Thus Sara called Abraham lord, although she was not a servant but a wife. …

Discourses Against the Arians 2.3-4 ↗