It comes directly from scripture from any Christians who are allowed to read scripture.
Matthew 9:24
He said, “Go away, for the girl is not dead but sleeping.” And they laughed at him.
Mark 5:39
And when he had entered, he said to them, “Why are you making a commotion and weeping? The child is not dead but sleeping.”
1 Thessalonians 4:13
But we do not want you to be uninformed, brothers, about those who are asleep, that you may not grieve as others do who have no hope. For since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have fallen
asleep. For this we declare to you by a word from the Lord, that we who are alive, who are left until the coming of the Lord, will not precede those who have fallen
asleep.
John 11:11
After saying these things, he said to them, “Our friend Lazarus has fallen asleep, but I go to awaken him.”
Matthew 27:52
The tombs also were opened. And many bodies of the saints who had fallen asleep were raised,
Psalm 13:3
Consider and answer me, O Lord my God; light up my eyes, lest I sleep the sleep of death,
Ephesians 5:14
For anything that becomes visible is light. Therefore it says, “Awake, O sleeper, and arise from the dead, and Christ will shine on you.”
Luke 8:52
And all were weeping and mourning for her, but he said, “Do not weep, for she is not dead but sleeping.”