Regret Is Repentance: An Islamic Perspective Explained
Question

I have decided to repent, because I have given up sin and decided not to go back to it. But I do not feel any regret in my heart. How can I attain regret, as it is difficult to achieve, because regret is not an action, and is not possible, because it is a reaction, not an action, and reactions are not voluntary. So why is it important to feel regret , when it is not an action that a person can do (it is just a feeling), and he is not able to do that? Should I pray to Allah to instil regret in my heart?
Praise be to Allah.The Essential Conditions for Valid Repentance
The conditions of valid repentance are as follows:

Giving up the sin
Regretting what one has done in the past
Resolving not to go back to it.

If the sin involved transgressing against people’s wealth, honour or lives, then there is a fourth condition, which is seeking forgiveness from the person who was wronged, or giving him his dues.
The Role of Regret in Islamic Repentance
Regret is a main condition, or the greatest aspect, of repentance. Hence the Messenger (blessings and peace of Allah be upon him) said: “Regret is repentance.” (Classed as authentic by Al-Albani in Sahih Ibn Majah)
One of the scholars even said:
Regret is sufficient to achieve repentance, for it implies giving up the sin and resolving not to go back to it, which stem from regret and do not occur independently of it. (End quote from Fat-h Al-Bari, 13/471)
Al-Qari (may Allah have mercy on him) said:
“Regret is repentance”: because this will lead to the other essential components of repentance – namely giving up the sin and resolving not to go back to it, and restoring people’s rights wherever possible.… What is meant is remorse for having committed the sin because it is a sin, and for no other reason.” (End quote from Mirqat Al-Mafatih,  4/1637)
What is meant by regret (Nadam) is sorrow, or deep sorrow, as is stated in Lisan Al-`Arab, (1/79, 6/4386)
The author explained regret as meaning sadness, then explained sadness as meaning sorrow or extreme sorrow.
In the words of Al-Qari (may Allah have mercy on him) quoted above, he explains regret as meaning remorse – that is, sorrow – for having committed the sin because it is a sin, and for no other reason.
What this means is that everyone who feels sorrow for having committed a sin has attained the regret that is referred to in the case of repentance. If this regret is sincere, then the sinner will give up the sin and will resolve not to do it again. Thus his repentance will be complete and will have met all the necessary conditions.
Based on that, everyone who gives up a sin because it is disobedience to Allah, may He be Exalted – in other words, out of fear of Allah and in obedience to Him – and hates the fact that he fell into sin and disobeyed the Lord of the Worlds, and wishes that he had obeyed Allah instead of disobeying Him, and resolves not to do it again, has definitely attained regret, and regret is what made him give up the sin.
The Process of Repentance: Knowledge, Awareness, and Action
Al-Ghazali (may Allah have mercy on him) said in Ihya’ `Ulum Ad-Din (4/4):
Repentance is something that evolves from one stage to another in three stages: knowledge, awareness and action. Knowledge is the first, awareness is the second and action is the third.
The first leads to the second, and the second leads to the third in an inevitable sequence as ordained by Allah.
As for knowledge, it means coming to know of the great harm that sins may cause and the fact that sins form a barrier between a person and everything that he loves and aspires for.
Once he becomes certain of this knowledge at a level of certainty that overwhelms him, there will result from this knowledge remorse and pain in the heart for missing out on what he loves and aspires to, because when the heart realises what he has missed out on of what he loves, there will be pain. If his missing out on it was the result of some deed that he did, then he will feel sorrow for doing the deed that caused him to miss out on that. This pain is called regret.
Once this pain becomes so intense that it overwhelms the heart, it will lead to another emotion in the heart, which is called resolution and the will to do something that is connected to the present, the past and the future.
With regard to the present, he will resolve to give up this sin that he was committing.
With regard to the future, he will resolve to refrain for the rest of his life from that sin that caused him to miss out on what he loves and aspires to.
With regard to the past, he will resolve to rectify the situation and make up for what he missed out on, if it can be rectified.
… Knowledge, regret and resolution have to do with keeping away from sin now and in the future, and rectifying what happened in the past, and all of that together is called repentance (Tawbah).
The word repentance is often used to refer to regret only, and awareness and knowledge are regarded as precursors, whilst giving up the sin is regarded as being the result and outcome. Based on that, we may understand what the Prophet (blessings and peace of Allah be upon him) meant when he said: “Regret is repentance,” because regret cannot take place unless one attains knowledge that leads to it, and it cannot but be followed by resolution, so regret has a precursor and an outcome. (End quote)
He also said (3/144):
If fear results from something that one did in the past, it will lead to regret, and regret will lead to resolution. The Prophet (blessings and peace of Allah be upon him) said: “Regret is repentance.” (End quote)
Overcoming Doubts about Repentance
Thus it becomes clear that your giving up the sin and resolving not to go back to it are indicative of the occurrence of regret in your heart. So you should ignore these whispers of the devil by means of which he wants to make you think that you have not repented yet, or that repentance is impossible, or that you will never be able to repent, which will create despair and hopelessness and make you think that the gate of repentance is closed to you.
We ask Allah, may He be exalted, to protect us all from the accursed devil, and to enable us to repent sincerely.
And Allah knows best.