Genesis 4:14-15
NRSV
14 Today you have driven me away from the soil, and I shall be hidden from your face; I shall be a fugitive and a wanderer on the earth, and anyone who meets me may kill me.”
15 Then the LORD said to him, “Not so![a] Whoever kills Cain will suffer a sevenfold vengeance.” And the LORD put a mark on Cain, so that no one who came upon him would kill him. (NRSV)
[a] Gk Syr Vg: Heb Therefore
KJV
14 Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me.
15 And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him. (KJV)
Of whom was Cain afraid? See Biblical evidence that people are not descended from a single male ancestor. — Bruce
Ron Abel, in Wrested Scriptures, says that there were no other humans outside Adam's family, and therefore he must have been afraid of "his brethren". See at Pre-Adamic Humans for an outline of his reasoning.
