The Creed of the Council of Toledo (AD 675) has this
We also confess that the Son was born, but not made, from the substance of the Father, without beginning, before all ages, for at no time did the Father exist without the Son, nor the Son without the Father. Yet the Father is not from the Son, as the Son is from the Father, because the Father was not generated by the Son but the Son by the Father. The Son, therefore, is God from the Father, and the Father is God, but not from the son. He is indeed the Father of the Son, not God from the Son; but the latter is the Son of the Father and God from the Father. Yet in all things the Son is equal to God the Father, for He has never begun nor ceased to be born. We also believe that He is of one substance with the Father; wherefore He is called homoousios with the Father, that is of the same being as the Father, for homos in Greek means ‘one’ and ousia means ‘being’, and joined together they mean ‘one in being’. We must believe that the Son is begotten or born not from nothing or from any other substance, but from the womb of the Father, that is from His substance. Therefore the Father is eternal, and the Son is also eternal. If He was always Father, He always had a Son, whose Father He was, and therefore we confess that the Son was born from the Father without beginning. We do not call the same Son of God a part of a divided nature, because He was generated from the Father, but we assert that the perfect Father has begotten the perfect Son, without diminution or division, for it pertains to the Godhead alone not to have an unequal Son. This Son of God is also Son by nature, not by adoption; of Him we must also believe that God the Father begot Him neither by an act of will nor out of necessity, for in God there is no necessity nor does will precede wisdom.