Rashi

ויצא קין AND CAIN WENT AWAY — He went away in pretended humility as though he would deceive the Most High (Genesis Rabbah 22:13). בארץ נוד IN THE LAND OF NOD — In the land where all exiles wander about. קדמת עדן ON THE EAST OF EDEN — Thereto his father went into exile when he was driven out from the Garden of Eden. as it is said, (3:24) “And He placed in the east of the Garden of Eden” a watch on the road that leads to the entrance of the Garden, from which one may infer that Adam was there (in the East) (Genesis Rabbah 21:9). Indeed, we find, also, that the Eastern quarter always forms a place of refuge for murderers, as it is said, (Deuteronomy 4:41) “Then Moses set aside three cities of refuge towards the place of sun-rise [that a murderer might flee thither].” Another explanation of בארץ נוד IN THE LAND OF NOD — (taking נוד in the sense of “movement”) — wherever he went the earth quaked beneath him, and people said, “Turn away from him: this is the man who killed his brother” (Midrash Tanchuma, Bereshit 9).