Genesis 6:2

6:2 the sons of God saw that the daughters of humankind were beautiful. Thus they took wives for themselves from any they chose.

Genesis 6:4

6:4 The Nephilim were on the earth in those days (and also after this) when the sons of God were having sexual relations with the daughters of humankind, who gave birth to their children. They were the mighty heroes of old, the famous men.