1 Samuel 3:8-10 New Revised Standard Version (NRSV)
8 The Lord called Samuel again, a third time. And he got up and went to Eli, and said, “Here I am, for you called me.” Then Eli perceived that the Lord was calling the boy. 9 Therefore Eli said to Samuel, “Go, lie down; and if he calls you, you shall say, ‘Speak, Lord, for your servant is listening.’” So Samuel went and lay down in his place.
10 Now the Lord came and stood there, calling as before, “Samuel! Samuel!” And Samuel said, “Speak, for your servant is listening.”