1 Samuel 3:8-10

So the LORD called a third time, and once more Samuel got up and went to Eli. “Here I am. Did you call me?” Then Eli realized it was the LORD who was calling the boy. So he said to Samuel, “Go and lie down again, and if someone calls again, say, ‘Speak, LORD, your servant is listening.’” So Samuel went back to bed. And the LORD came and called as before, “Samuel! Samuel!” And Samuel replied, “Speak, your servant is listening.”