Tertullian

“ I should not hesitate, indeed, to call the tree the son or offspring of the root, and the river of the fountain, and the ray of the sun; because every original source is a parent, and everything which issues from the origin is an offspring. Much more is (this true of) the Word of God, who has actually received as His own peculiar designation the name of Son. But still the tree is not severed from the root, nor the river from the fountain, nor the ray from the sun; nor, indeed, is the Word separated from God. ”

“ Everything which proceeds from something else must needs be second to that from which it proceeds, without being on that account separated. Where, however, there is a second, there must be two; and where there is a third, there must be three. Now the Spirit indeed is third from God and the Son; just as the fruit of the tree is third from the root, or as the stream out of the river is third from the fountain, or as the apex of the ray is third from the sun. ”

“ This will be the prolation, taught by the truth, [12] the guardian of the Unity, wherein we declare that the Son is a prolation from the Father, without being separated from Him. For God sent forth the Word, as the Paraclete also declares, just as the root puts forth the tree, and the fountain the river, and the sun the ray. ”