In one of his khutbahs, Abu Bakr (radiyallahu anh), after praising Allah Taala and Rasulullah (sallallahu alayhi wa sallam), said the following:
Be careful! Every deed, every action has a culmination, a point where it reaches saturation. Whoever reaches that point, it will be sufficient for them. Whoever does something for Allah, Allah will be sufficient to them. What falls on you is your duty to be steadfast and moderate in your affairs. The middle way will surely lead a person to achieve his goal more securely.
Be careful! A person without iman has no religion. Just as there is no reward for a person who does something other than for the sake of Allah, the deed of a person who does something without setting his intention first, is invalid (there is no reward for a deed performed by a person without determining his intention for that deed, in his heart, in the first place).
Be careful! In the Book of Allah, rewards are promised to those who struggle for the cause of Allah. But know that it is not suitable for a person to think that this reward is intended only for them. Rather, it is a trade that Allah has shown with which He has saved you from humiliation and attached the honour of this world and the Hereafter to it.
Allah Taala only accepts deeds done for His own sake. Your actions should be for His sake. Know that what will save you are your sincere deeds full of ikhlas. In the eternal Hereafter, what you will need is the worship and obedience you performed in this mortal world. Your obedience to Allah consists of correcting your mistakes and fulfilling your debts and duties.
O servants of Allah! Take heed from those who came and passed away before you. Where are the oppressors and the tyrants, the celebrated valiant men who were victorious in wars? Time has humiliated and destroyed them. Now their bones have rotten away, leaving behind memories of their evil deeds.
Where are the rulers who built on the face of the earth? They have now departed, their names and glory forgotten as if they never existed.
Know that Allah Taala has placed rights over them which will be demanded of them and for which they are responsible, while they are now cut off from lust and desires. Even though they have departed, their deeds remain behind. Their worldly wealth is now in the hands of others. We live as successors to them in this world. If we take lessons from them and find ourselves performing beneficial deeds, we will be saved. If we allow ourselves to become proud and haughty, we will be just like them.
Where are the beautiful faces deceived by their youth? They have returned to the soil. Their excess brought them to ruin. Where are those who built cities, surrounded them with walls, and left astonishing works within them? They left them to those who came after them. Their places of residence have turned upside down, and they now remain in the darkness of their graves.