This association with shirk is noteworthy for shirk is considered unforgivable if not repented of. God forgiveth not (the sin of) joining other gods to Him; but He forgiveth whom He pleaseth other sins that this: one who joins other gods with God hath strayed far, far away.
Coming back to the above question, regarding the signs that Allah SWT has accepted a person's repentance is when his attitude and character change, his soul became closer and his love for the mosque increases, his manners and language improve, he feels happy when worshipping and he continues to seek for forgiveness ...
“O Allah, wash off my sins with the [melted] water of ice and snow, and purify my heart of sins, just as white clothes are cleansed of filth.” Imam Bukhari and Imam Muslim (rahimahumallah) have also recorded this du'a in a lengthier narration which comprises of other du'as as well.
Expiates your sins
That's why most scholars advise you to give Sadaqah after every sin you commit; in the hope that this act of Sadaqah removes the sin from your scale on the Day of Judgment.
The Quran declares: Say: "O my Servants who have transgressed against their souls! Despair not of the Mercy of Allah: for Allah forgives all sins: for He is Oft-Forgiving, Most Merciful.
Repent sincerely by verbalizing 'astaghfirullah,' which means, “I seek forgiveness from Allah.” Resolve to never commit the sin again. Repair: If the sin involved wronging someone, make reparations by seeking their forgiveness and recompensing them if possible.
If you want your minor and major sins forgiven say “Astagh-fi-rulla-hal Azeem, al-lazi la ilaha il-la Huwal-Hay-yul-Qayyum wa aa-tubu i-laih''.
Surah Al-Furqan, verse 74. And those who say, “Our Lord, grant us from among our wives and offspring comfort to our eyes and make us an example for the righteous.” May Allah grant us willpower so that we could stay away from these grave sins and accept our repentance by saying Astaghfaar all the time.
When you regret your sins, feel sad for having committed them and feel pain when you remember them, these are signs of faith and sincere repentance. However, after repenting, Satan will cause you to doubt the Almighty's Mercy. Don't despair. Don't fall for his trick!
The first step for the sinner is sincere repentance. Sincere repentance includes having remorse over your actions, as well as a resolute determination not to fall back into the sin.
Allah is the Most Merciful. Here are some verses of Qur'an regarding His Mercy: “Say My slaves who have transgressed against themselves (by committing evil deeds and sins) Do not despair of the Mercy of Allah: verily He forgives all sins. Truly He is Oft-Forgiving, Most Merciful.”
Shirk is ascribing partners with Allah, and is indeed the greatest of all sins. It is stated in the Noble Qur'an: “Allah forgives not that partners should be set up with Him, but He forgives anything else, to whom He pleases. To set up partners with Allah is to devise a sin most heinous indeed” (Qur'an 4:48).
I believe that God can forgive all sins provided the sinner is truly contrite and has repented for his or her offenses. Here's my list of unforgivable sins: ÇMurder, torture and abuse of any human being, but particularly the murder, torture and abuse of children and animals.
To lose hope or faith in Allah and to believe that Allah would not save one on the day of Judgement. It's also considered a sin to have for an unmarried man and woman to have a sexual relationship or commit adultery. Homosexuality is also considered a sin in Islam, for both men and women. To withhold Zakat.
Ch 112 Surah Al-Ikhlas or Al-Tawhid
When a person recites this Surah 100 times, all his sins for the past 25 years are forgiven (except the sins of killing an innocent person or usurping the property of people). The one who recites it 1000 times will not die unless he sees his place in Jannah.
Powerful Dua for forgiveness ᴴᴰ - by Saad Al Qureshi سُبْحَانَکَ إِنِّي ظَلَمْتُ نَفْسِي فَاغْفِرْ لِي فَإِنَّهُ لا يَغْفِرُ الذُّنُوبَ إِلا أَنْتَ Glorified be Thou! Behold, I have wronged myself. So forgive thou me. Indeed, non forgiveth sins but Thou.
Be open and honest with God through prayer and admit that you have made mistakes. Once you have confessed your sins, ask for help. “By this ye may know if a man repenteth of his sins—behold, he will confess them and forsake them” (D&C 58:43).
Abu Huraira reported Allah's Apostle as saying: “Allah has decreed for every son of Adam his share of zina, which he will inevitably commit. The zina of the eyes is looking, the zina of the tongue is speaking, one may wish and desire, and the private parts confirm that or deny it.”
The Holy Prophet (PBUH) used to do istighfar 70 -100 times. So we human beings who have done so many sins and displeased ALLAH (SWT ) with our bad deeds must ask forgiveness from ALLAH and should say Istighfar at least 100 times every day.
If forgiving someone more than once or twice seems unreasonable, just remember how often God forgives you. He doesn't put a limit on how many times you turn to him with your sincere heart, humbly seeking forgiveness. He's just glad you've returned. May we do our best to model our forgiveness after God's example.
Always have faith and be persistent in loving and forgiving people. When you fail and give in to temptation, be sure to pray. Pray for forgiveness, get back on your feet and continue your life with Jesus. When God forgives you, he completely forgets that you ever sinned.