The Proof of Islam (may God’s mercy be on him) wrote in his book The Beginning of Guidance [Bidayat al-Hidaya], in the chapter “Preparing for the Ritual Prayers”:
You should not neglect your time or use it haphazardly; on the contrary, you should bring yourself to account, structure your litanies and other practices during each day and night, and assign to each period a fixed and specific function. This is how to bring out the spiritual blessing [baraka] in each period. But if you leave yourself adrift, aimlessly wandering as cattle do, not knowing how to occupy yourself at every moment, your time will be lost. It is nothing other than your life, and your life is the capital that you make use of to reach perpetual felicity in the proximity of God the Exalted. Each of your breaths is a priceless jewel, since each of them is irreplaceable and, once gone, can never be retrieved. Do not be like the deceived fools who are joyous because each day their wealth increases while their life shortens. What good is an increase in wealth when life grows even shorter? Therefore, be joyous only for an increase in knowledge or in good works, for they are your two companions who will accompany you in your grave when your family, wealth, children, and friends stay behind.
[Imam al-Ghazali] also wrote (may God’s mercy be on him),
Know that a night and a day comprise twenty-four hours; therefore do not sleep more than eight hours, for it should suffice you, for if you were to live sixty years, for instance, you would have wasted twenty, which is one third.
And he said:
If you do [remember death and prepare for its coming], you will know endless joy when death arrives. Whereas if you are complacent and procrastinate, death will come to you at an unforeseen moment and you will know regrets without end. At dawn people are grateful for the traveling they did by night. With death, certainty comes to you; you will surely have its experience, in time.
This book, though shorter than many lengthier treatises dealing with the same matter, contains what should be enough for the intelligent alert believer who is active in worship. A Shadhili scholar once said:
What Imam al-Ghazali (may God have mercy on him) has included in ‘The Beginning of Guidance‘ is sufficient for a sufi beginner; what he has included in ‘The Way of the Worshippers‘ [Minhaj al-‘Abidin] suffices the one in the middle; and ‘The Revival of the Religious Sciences‘ [Ihya’ ‘Ulum al-Din] is enough for the one near the end of the path.
The matter is this way for whoever is fair in his judgment and aims to adorn himself with the best of virtues and attributes. God grants success, there is no other Lord. How excellent are the poet’s words:
Gather provision for the inescapable.
Mankind has an appointment at the Resurrection.
Will it please you to be with those whose
provision is abundant while yours is amiss?
Also the famous poem which begins:
I see that daylight illumines for you
the upright road from which you swerve.
And where he says:
We fall prey to the illusion of the green branches
of hope, which never bear fruit.
This is a blessed poem belonging to a certain man from Yemen. Our master Shaykh ‘Umar al-Mihdar ibn ‘Abd al-Rahman used to like it and so did Shaykh Fadl ibn ‘Abdallah al-Tarimi al-Shihri, may God have mercy on them and spread their benefit and that of all virtuous servants of God.
-Imam Abdallah al-Haddad, Knowledge and Wisdom