The serpent seed doctrine is the false idea that Cain was the offspring of Eve and Satan, the serpent. There is a reference to that false idea in the Gospel of Philip, a non-canonical writing that is thought to have been written between 150 and 350 A.D.
There is no serpent seed doctrine in the Bible. Satan presented Eve with a temptation that involved fruit. Through Satan, sin entered the world. Thanks be to God for sending Jesus, his Son, to destroy the work of Satan (1 John 3:8).