1 Samuel 3:7-9

Now Samuel did not yet know the LORD, nor had the word of the LORD yet been revealed to him. So the LORD called Samuel again for the third time. And he arose and went to Eli and said, “Here I am, for you called me.” Then Eli discerned that the LORD was calling the boy. And Eli said to Samuel, “Go lie down, and it shall be if He calls you, that you shall say, ‘Speak, LORD, for Your servant is listening.’ ” So Samuel went and lay down in his place.