Then the LORD said to Cain, "Where is Abel your brother?" He said, "I do not know. Am I my brother's keeper?"
Genesis 4:9
Surrounding context
4:8 Now Cain talked with Abel his brother; and it came to pass, when they were in the field, that Cain rose up against Abel his brother and killed him.
4:9 Then the LORD said to Cain, "Where is Abel your brother?" He said, "I do not know. Am I my brother's keeper?"
4:10 And He said, "What have you done? The voice of your brother's blood cries out to Me from the ground.