Is Sleeping In a Sin?

This is taken from George Muller's autobiography:

I want to encourage all believers to get into the habit of rising early to meet with God.  how much time should b allowed for rest?  No rule of universal application can be given because all persons do not require the same amount of sleep.  Also the same persons, at different times, according to the strength or weakness of their body, may require more or less.  most doctors agree that healthy men do not require more than between six or seven hours of sleep, and females need no more than seven or eight hours.
Children of God should be careful not to allow themselves too little sleep since few men can do with less than six hours of sleep and still be well in body and mind.  As a young man, before I went to the university, I went to bed regularly at ten and rose at four, studied hard, and was in good health.  Since I have allowed myself only about seven hours, I have been much better in body and in nerves than when I spent eight or eight and a half hours in bed.
Someone may ask, "But why should I rise early?"  To remain too long in bed is a waste of time.  Wasting time is unbecoming a saint who is bought by the precious blood of Jesus.  His time and all he has is to be used for the Lord.  If we sleep more than is necessary for the refreshment of the body, it is wasting the time the Lord has entrusted us to be used for His glory, for our own benefit, and for the benefit of the saints and unbelievers around us.
Just as too much food injures the body, the same is true regarding sleep.  Medical persons would readily agree that lying longer in bed than is necessary to strengthen the body actually weakens it.
It also injures the soul.  Lying too long in bed not merely keeps us from giving the most precious part of the day to prayer and meditation, but this sloth leads also to many other evils.  Anyone who spends one, two, or three hours in prayer and meditation before breakfast will soon discover the beneficial effect early rising has on the outward and inward man.