Psalm 121:4 (NASB)
Behold, He who watches over Israel will neither slumber nor sleep.

Isaiah 40:25–26, 28–31 (NIV)
25 “To whom will you compare me? Or who is my equal?” says the Holy One.
26 Lift up your eyes and look to the heavens: Who created all these? He who brings out the starry host one by one
and calls forth each of them by name. Because of his great power and mighty strength, not one of them is missing.
28 Do you not know? Have you not heard? The Lord is the everlasting God, the Creator of the ends of the earth.
He will not grow tired or weary, and his understanding no one can fathom. 29 He gives strength to the weary
and increases the power of the weak. 30 Even youths grow tired and weary, and young men stumble and fall; 31 but those who hope in the Lord will renew their strength. They will soar on wings like eagles; they will run and not grow weary, they will walk and not be faint.

Mark 4:26-27 (NIV)
26 He also said, “This is what the kingdom of God is like. A man scatters seed on the ground. 27 Night and day, whether he sleeps or gets up, the seed sprouts and grows, though he does not know how.

Quotes:
“It’s a surrender, a laying down of arms. Whatever plans you’re making, whatever work you’re up to your ears in, whatever pleasures you’re enjoying, whatever sorrows or anxieties or problems you’re in the midst of, you set them aside, find a place to stretch out somewhere, close your eyes, and wait for sleep. All the things that make you the particular person you are stop working—your thoughts and feelings, the changing expressions of your face, the constant moving around, the yammering will, the relentless or not so relentless purpose. But all the other things keep on working with a will and purpose of their own. You go on breathing in and out. Your heart goes on beating. … Whether you’re just or unjust, you have the innocence of a cat dozing under the stove. Whether you’re old or young, homely or fair, you take on the serenity of marble. You have given up being in charge of your life. … It is a rehearsal for the final laying down of arms.” —Frederich Buechner

“We are not God. Once a day God sends us to bed like patients with a sickness. The sickness is a chronic tendency to think we are in control and that our work is indispensable. To cure us of this disease God turns us into helpless sacks of sand once a day. Sleep is a parable that God is God and we are mere men. … Sleep is like a broken record that comes around with the same message every day: Man is not sovereign. Man is not sovereign. Man is not sovereign. Don’t let the lesson be lost on you. God wants to be trusted as the great worker who never tires and never sleeps. He is not nearly so impressed with our late nights and early mornings as he is with the peaceful trust that casts all anxieties on him and sleeps.” —John Piper