"Our Churches, with common consent, do teach that the decree of the Council of Nicaea concerning the Unity of the Divine Essence and concerning the Three Persons, is true and to be believed without any doubting; that is to say, there is one Divine Essence which is called and which is God: eternal, without body, without parts, of infinite power, wisdom, and goodness, the Maker and Preserver of all things, visible and invisible; and yet there are three Persons, of the same essence and power, who also are coeternal, the Father the Son, and the Holy Ghost. And the term "person" they use as the Fathers have used it, to signify, not a part or quality in another, but that which subsists of itself.
They condemn all heresies which have sprung up against this article, as the Manichaeans, who assumed two principles, one Good and the other Evil- also the Valentinians, Arians, Eunomians, Mohammedans, and all such. They condemn also the Samosatenes, old and new, who, contending that there is but one Person, sophistically and impiously argue that the Word and the Holy Ghost are not distinct Persons, but that "Word" signifies a spoken word, and "Spirit" signifies motion created in things." (Augsburg Confession, Article I: Of God)
"HERESIES. Therefore we condemn the [unbelieving] Jews and Mohammedans, and all those who blaspheme that sacred and adorable Trinity. We also condemn all heresies and heretics who teach that the Son and Holy Spirit are God in name only, and also that there is something created and subservient, or subordinate to another in the Trinity, and that their is something unequal in it, a greater or a less, something corporeal or corporeally conceived, something different with respect to character or will, something mixed or solitary, as if the Son and Holy Spirit were the affections and properties of one God the Father, as the Monarchians, Novatians, Praxeas, Patripassians, Sabellius, Paul of Samosata, Aetius, Macedonius, Anthropomorphites, Arius, and such like, have thought." (The Second Helvetic Confession, Ch. III - OF God, His Unity and Trinity)
"This doctrine of the Holy Trinity hath always been defended and maintained by the true Church, since the times of the Apostles to this very day, against the Jews, Mohammedans, and some false Christians and heretics, as Marcion, Manes, Praxeas, Sabellius, Samosatenus, Arius, and such like, who have been justly condemned by the orthodox fathers." (The Belgic Confession, Art. IX.)