Abu Yusuf's Letter to the caliph Harun ar-Rashid
Commander of the Believers, Allah has invested you with a great matter, whose reward is the greatest reward, and whose punishment is the greatest punishment: He has entrusted you with the affair of the Community of Believers. Day and night you build for many people, of whom Allah made you the shepherd, whom He has confided to your care and tried you with, and of those whose affairs He has made you the administrator. A structure not founded on piety shall not abide, for Allah will attack its foundations and cause it to fall on him who built it and trusted in it against Him. Therefore do not waste what Allah has entrusted you with: the matter of this Community and these subjects, for power to act is by Allah's leave.
Do not put off the work of today until tomorrow, for if you do, you waste. Death is without hope, so go to death with deeds, for there are no deeds after death. Shepherds of men must settle with their Master, as a shepherd must settle with his; therefore establish the right in what Allah has set you over and entrusted you with for an hour. The happiest shepherd on the Day of Resurrection will be he whose flocks were happy with him. Do not deviate, and thus cause your subjects to deviate, and beware of giving orders in passion or punishing with anger! When confronted by the matter of this world and the matter of the next, choose the next world, for it will abide and this world will pass away. Act cautiously, in fear of Allah, and where Allah's command is concerned, let people be equal in your sight, whether they are near or far from you. When you are on Allah's side, fear no one's blame. Be wary - and wariness is a matter of the heart, not of the tongue. Fear Allah, for piety is only fear of Allah, and Allah keeps him who fears Him.
Act for a term delayed, and road travelled and a way taken, and an act preserved, and a goal attained, for that is the true stopping place; the grand station, where hearts shall fly and arguments be cut off, by the might of a king whose power is overwhelming, for this is (so certain that it is) as if it had already been. There will be requited with sorrow and regret those who knew but did not act, on the Day when feet shall drag and colours change, the day of long standing and severe accounting. Allah, blessed is He and Exalted, has said in His Book:
"A day with Allah is as a thousand years of what you reckon." [Al-Qur'aan 22:47]
And
"On the day when they see that which they are threatened, it will appear to them that they had not stayed for more than an hour of a day." [Al-Qur'aan 46:35]
A lack for mistakes that are not found small, alas for useless regrets! Only the difference of a night and a day will wear out every new thing, and make imminent every remote matter, and being the fulfilment of every thing promised, and Allah will pay every should what it has earned - and surely Allah is swift at the accounting and He judges His servants by their acts, not by their rank.
The Prophet, peace be upon him, has said: "No one shall retire on the Day of Judgement until he has been asked about four matters: on his knowledge and what he did with it, on his life and how he passed it, on his money and how he spent it, and on his body, and how he used it."
Therefore, Prince of the Believers, prepare the response for these questions, and what you have done establish securely, for tomorrow you must recite the answers.
I advise you, O Commander of the Believers, to keep what Allah has entrusted to you, and to guard the flock He has given you, and to regard it all as His for His sake, for if you do not, the easy path of guidance will become hard, and your eye will be blind to it; its landmarks will be effaced, and its width will be narrow for you, so that you reject what you see and see what you should reject. Contend with your self (nafs) so as to obtain victory for it, and not against it. Beware of causing loss to the flock which its Master will require to make good, causing you loss. A house cane only be buttressed before it falls. Do not neglect to take charge of that which Allah has entrusted you, and you will not be neglected. Your time in the world will not be wasted, and Allah in His grace and mercy and goodness made those in charge of affairs His vicegerents on His earth, and given light to His subjects; the light which he causes to shine on those in charge of affairs is in applying the legal punishment and rendering justice to His people. The violence of the shepherd causes loss to the flock, and the aid he seeks from those who are untrustworthy of confidence causes general ruin. Nothing is dearer to Allah than doing good, and nothing more hateful to Him than corruption, while to act sinfully is to reject His Grace.
I have written for you what you have ordered, and explained it and make exposition of it, so ponder it and apply yourself to it and reread it until it is yours, for I have exerted myself for you, and neglected no advice for you and the Muslims, seeking Allah's favour and reward and fearing His chastisements.
May Allah assist you to that which will be pleasing to Him, and best for you!