1 Samuel 3:7-9

Now Sh'mu'el didn't yet know ADONAI; the word of ADONAI had not yet been revealed to him.

ADONAI called, "Sh'mu'el!" again, a third time. He got up, went to 'Eli and said, "Here I am - you called me." At last 'Eli realized it was ADONAI calling the child.

So 'Eli said to Sh'mu'el, "Go, and lie down. If you are called again, say, 'Speak, ADONAI; your servant is listening.' Sh'mu'el went and lay down in his place.