And the LORD called Samuel again the third time. So he arose and went to Eli, and said, "Here I am, for you did call me." Then Eli perceived that the LORD had called the boy.
1 Samuel 3:8
Surrounding context
3:7 (Now Samuel did not yet know the LORD, nor was the word of the LORD yet revealed to him.)
3:8 And the LORD called Samuel again the third time. So he arose and went to Eli, and said, "Here I am, for you did call me." Then Eli perceived that the LORD had called the boy.
3:9 Therefore Eli said to Samuel, "Go, lie down; and it shall be, if He calls you, that you must say, "Speak, LORD, for Your servant hears."' So Samuel went and lay down in his place.