1 Samuel 3:7-9

Now Samuel did not yet know the LORD, because the word of the LORD had not yet been revealed to him.

Once again, for the third time, the LORD called to Samuel. He got up, went to Eli, and said, “Here I am, for you have called me.” Then Eli realized that it was the LORD who was calling the boy.

“Go and lie down,” he said to Samuel, “and if He calls you, say, ‘Speak, LORD, for Your servant is listening.’” So Samuel went and lay down in his place.