the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
“Tawbah” means repentance. A person repents after knowingly committing a sin. Sincere repentance has the following conditions:
1. The person must recognize that he or she has committed a sin and truly regret having done so.
2. The person must have a sincere resolve never to commit the sin again.
3. The person must turn to God in humility and ask for forgiveness.
4. If the sin had caused harm to someone else, the person must make every attempt to redress the harm.
If a person repents with true sincerity and conviction, then the reward is Allah’s forgiveness. Repentance is a form of worship. Allah loves when His servants turn to Him alone for forgiveness.
“Istighfâr”, by contrast, is simply the act of asking Allah for forgiveness. It includes saying “Astaghfirullâh”. It is a supplication and a remembrance of Allah that can be engaged in at any time. It does not have to be said only after knowingly committing a sin.
The Prophet (peace be upon him) said: “Verily I ask Allah for forgiveness more than seventy times a day.” [Sahîh al-Bukhârî]
There are numerous verses in the Qur’an regarding this practice. Allah says: “But ask forgiveness of your Lord, and turn unto him (in repentance): for my Lord is indeed full of mercy and loving-kindness.” [Sûrah Hûd: 90]
Allah also says: “If they had only, when they were unjust to themselves, come unto thee and asked Allah’s forgiveness and the Messenger had asked forgiveness for them, they would have found Allah indeed oft-returning, most merciful.” [Sûrah al-Nisâ’: 64]
Source: Islam Today