Tertullian (De Carne Christi 6)

The whole section is worth reading, but here's a portion of it:

"But the Lord Himself at that very time appeared to Abraham among those angels without being born, and yet in the flesh without doubt, in virtue of the before-mentioned diversity of cause. You, however, cannot admit this, since you do not receive that Christ, who was even then rehearsing how to converse with, and liberate, and judge the human race, in the habit of a flesh which as yet was not born, because it did not yet mean to die until both its nativity and mortality were previously (by prophecy) announced. Let them, then, prove to us that those angels derived their flesh from the stars. If they do not prove it because it is not written, neither will the flesh of Christ get its origin therefrom, for which they borrowed the precedent of the angels" (Tertullian, De Carne Christi 6).