During the time young Samuel was minister, under Eli, to God in the Temple of the Ark, the word of God was scarce and vision infrequent. One night Eli was asleep in his usual place in the Temple. Then God called to Samuel. Samuel answered, “Here I am.” Samuel ran to Eli and said, “Here I am. You called me.” “I did not call you,” Eli answered. “Go back to sleep.” So Samuel went back to sleep. But again the Lord called Samuel, who rose and went again to Eli. “Here I am,” he said. “You called me.” But Eli answered, “I did not call you, my son. Go back to sleep.”
Samuel did not yet recognize the voice, since God had not yet been revealed to him. God called Samuel again, for the third time. Getting up and going to Eli, he said, “Here I am. You called me.” Then Eli understood that God was calling the youth.
So he said to Samuel, “Go to sleep, and if you are called, reply, ‘Speak, Lord, for your servant is listening.” When Samuel went to sleep in his place, the Lord came and called out as before: Samuel, Samuel! This time Samuel answered, “Speak, Lord, for your servant is listening.”
I Samuel 3:1-10 (paraphrased)
(That 'Voice' comes, not only at night, but also when we are 'asleep' while awake.)