The Forgotten Books of Eden, by Rutherford H. Platt, Jr., , at sacred-texts.com
A third son is born to Adam and Eve.
AND Eve brought forth a son perfectly beautiful in figure and in countenance. His beauty was like that of his father Adam, yet more beautiful.
2 Then Eve was comforted when she saw him, and remained eight days in the cave; then she sent her daughter unto Adam to tell him to come and see the child and name him. But the daughter stayed in his place by the body of her brother, until Adam returned. So did she.
3 But when Adam came and saw the child's good looks, his beauty, and his perfect figure, he rejoiced over him, and was comforted for Abel. Then he named the child Seth, that means, "that God has heard my prayer, and has delivered me out of my affliction." But it means also "power and strength."
4 Then after Adam had named the child, he returned to the Cave of Treasures; and his daughter went back to her mother.
5 But Eve continued in her cave, until forty days were fulfilled, when she came to Adam, and brought with her the child and her daughter.
6 And they came to a river of water, where Adam and his daughter washed themselves, because of their sorrow for Abel; but Eve and the babe washed for purification.
7 Then they returned, and took an offering, and went to the mountain and offered it up, for the babe; and God accepted their offering, and sent His blessing upon them, and upon their son Seth; and they came back to the Cave of Treasures.
8 As for Adam, he knew not again his wife Eve, all the days of his life; neither was any more offspring born of them; but only those five, Cain, Luluwa, Abel, Aklia, and Seth alone.
9 But Seth waxed in stature and in strength; and began to fast and pray, fervently.