1 Samuel 3:7-9

Now Samuel did not yet know the Lord, neither had the word of the Lord been revealed to him.

And the Lord called Samuel again the third time. And he arose up and went to Heli,

And said: Here am I: for thou didst call me. Then Heli understood that the Lord called the child, and he said to Samuel: Go, and sleep: and if he shall call thee any more, thou shalt say: Speak, Lord, for thy servant heareth. So Samuel went, and slept in his place.