Allah Ta'aalaa says:
"O Believers.' Make taubah unto Allah Ta'aalaa a pure taubah."
Rasulullah Sallallahu alayhi wasallam said:
"O people! Make taubah unto Allah Ta'aalaa."
Muslim
Taubah (repentance) is the regret and sadness which arise in the heart when remembering a sin. For the validity of the taubah, shunning the sin, firmly resolving to abstain from it in future and controlling the nafs when it urges for the sin, are necessary.
The taubah means to return -- to return from the far side to the near side. It has a beginning and an end. The beginning(Ibtidaa) of taubah is the spreading of the rays of Noor-e-Ma'rifat (the Light of Divine Recognition) of the heart which thus realizes that the sin committed is a fatal poison which wroughts great spiritual disaster. This realization induces regret and fear which result in a true and sincere yearning to compensate for the sin. This yearning is to such a degree that shunning of the sin is immediate. Further, a firm resolve and intention are made to totally abstain from the sin in future. Along with this intention a full effort is made to compensate for the past shortcoming. When the result is this fruit of taubah pertaining to the past, present and future, then perfection of taubah has been acquired. This then is the end (Intihaa) of taubah.
It should be clear that taubah is Waajib (compulsory) upon every person because Allah Ta'aalaa addresses all Muslims in the Aayat:
"O Believers! Make taubah unto Allah, a pure taubah."
Since the reality of taubah is to regard sin as a fatal poison and disaster for the life of the Hereafter, and to firmly resolve to shun sin this much of taubah is part of Imaan it being waajib and necessary are apparent to every Mu'min. Hence, Allah Ta'aalaa says:
"He who makes taubah after his transgression arid reforms, verily Allah turns towards him."
Qur'aan
The meaning of this Aayat is:
Allah Ta'aalaa will forgive, have mercy upon and aid the person who after having sinned renders taubah according to the rule of the Shari'at and reforms his acts for the future, i.e. he abstains from all evil, practices in conformity with the Shari'at and remains firm on his taubah.
Taubah or repentance is to confess to Allah Ta'aalaa one's sins and to regret such commission. Resolve firmly to discharge all Huqooq-ul-Ibaad (rights of others) and other duties which are obligatory, but which have not been rendered. This intention should be immediately made and thereafter the actual fulfillment of such rights and duties put into motion. Alternatively, the pardon of those whose rights were usurped should be obtained. When a sin has been committed, immediately perform two Rak’ats Salaat with the intention of Taubah. One then has to offer repentance with both the tongue and heart. The taubah should be made fervently and vigorously. If one is unable to shed tears, then one's face should take on the appearance of a concerned and crying person while making taubah.
For the purpose of making taubah, recall your sins and then offer repentance in profusion. However, do not meditate about the sins committed or do not make vigorous attempts in a bid to remember what sins had been committed, for this attitude will create a barrier between the repenter and Allah Ta'aalaa. This constitutes an obstacle in the path of love and progress. After having made a sincere taubah, if previous sins come to mind then renew the taubah. Do not be too much concerned about sins for which taubah has already been made.
While making taubah there should be a degree of moderation in mentioning the sins. There is no need to recite a whole list of sins while making taubah. Seek forgiveness for all sins in general. According to the Hadith Shareef one should say:
"And, I repent of even such sins which you are more aware of."
"I repent of such sins which l am aware of and of such sins which I am unaware."
Pondering about sins is in actual fact destruction of time and diversion from the remembrance of Allah. However, one should make special taubah for sins which one recalls automatically. The real Goal is Allah Ta'aalaa and not the remembrance of sins neither the remembrance of acts of obedience. The purpose of remembering sins is to offer repentance. Hence, once taubah has been made, one should not deliberately and consciously ponder over sins thereby making such remembrance a definite purpose because this will engender the idea that Allah Ta'aalaa is displeased with one, and this is a dangerous idea.
Remember and reflect about the warnings sounded in the Qur'aan and Hadith in regard to sins. The pang of regret which enters the heart as a result of such reflection is in actual fact taubah.