But grant that these argumentations may be thought to be forced and founded on con jectures, if no dogmatic teachings have stood parallel with them which the Lord uttered in treating of divorce, which, permitted formerly, He now prohibits, first because “from the beginning it was not so,” like plurality of marriage; secondly, because “What God hath conjoined, man shall not separate,” —for fear, namely, that he contravene the Lord: for He alone shall “separate” who has “conjoined” (separate, moreover, not through the harshness of divorce, which (harshness) He censures and restrains, but through the debt of death) if, indeed, “one of two sparrows falleth not on the ground without the Father’s will.” Therefore if those whom God has conjoined man shall not separate by divorce, it is equally congruous that those whom God has separated by death man is not to conjoin by marriage; the joining of the separation will be just as contrary to God’s will as would have been the separation of the conjunction.
Tertullian, On Monogamy 9