Is repentance valid without regret for past sins, and what is the meaning of stipulating regret in repentance?

The conditions for a valid repentance are: abandoning the sin, regretting it, and resolving not to return to it. Additionally, if the repentance concerns injustices against people, it requires redressing the wrong with the aggrieved party. Allah has commanded sincere repentance, saying: ﴿O YOU WHO HAVE BELIEVED, REPENT TO ALLAH WITH SINCERE REPENTANCE.﴾ The predecessors defined sincere repentance as repentance after which one does not return to the sin, or regret and resolve not to return, or seeking forgiveness with the tongue, regret with the heart, and abstaining with the body.

Regret is the greatest pillar of repentance, for the Prophet, peace and blessings be upon him, said: «REGRET IS REPENTANCE.» This necessitates abandoning the sin and resolving not to return to it. To achieve regret, four things aid the servant: knowledge of Allah after ignorance of Him, remembrance of Allah after heedlessness of Him, fear of Allah's cunning after feeling secure from it, and hope in Allah's mercy after despairing of it.

As for the fruits of regret, they are: the continuous pain and sorrow of the heart over the sin, wishing not to return to it, abandoning the sin, and resolving not to return to it. Not returning to the sin is a condition for the completeness and benefit of repentance.

As for the fruits of resolving not to return to the sin, they are: closing the door to sin by avoiding bad company and tools that lead to disobedience, closing off pretexts that lead to sin by avoiding doubtful matters, performing the opposite of the sin, and opening up avenues that lead to righteous deeds and steadfastness in obedience.