Original: In Sotah 10b, Samael is Esau's guardian angel, and in the Sayings of Rabbi Eliezer, he is charged with being the one who tempted Eve, then seduced and impregnated her with Cain.
Simplified: In the Sayings of Rabbi Eliezer, he is said to be the one who tempted Eve, then seduced and impregnated her with Cain.