Dua of Prophet Adam
رَبَّنَا ظَلَمْنَا أَنفُسَنَا وَإِن لَّمْ تَغْفِرْ لَنَا وَتَرْحَمْنَا لَنَكُونَنَّ مِنَ الْخَاسِرِينَ
Rabbana zalamna anfusana wa-in lam taghfir lana wa-tarhamna lanakoonanna minal-khasireen.
"Our Lord, we have wronged ourselves, and if You do not forgive us and have mercy upon us, we will surely be among the losers."
(Quran, Surah Al-A'raf, 7:23)
The Master of Forgiveness
اللَّهُمَّ أَنْتَ رَبِّي لَا إِلَهَ إِلَّا أَنْتَ، خَلَقْتَنِي وَأَنَا عَبْدُكَ، وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَ مَا اسْتَطَعْتُ، أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ، أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ، وَأَبُوءُ بِذَنْبِي فَاغْفِرْ لِي فَإِنَّهُ لَا يَغْفِرُ الذُّنُوبَ إِلَّا أَنْتَ
Allahumma anta Rabbi la ilaha illa Anta, khalaqtani wa ana abduka, wa ana ‘ala ahdika wa wa’dika mastata’tu, a’udhu bika min sharri ma sana’tu, abu’u laka bi ni’matika ‘alayya, wa abu’u bidhanbi faghfir li fa-innahu la yaghfirudh-dhunuba illa Anta.
"O Allah, You are my Lord, there is no god but You. You created me, and I am Your servant, and I am on Your covenant and Your promise as much as I am able. I seek refuge in You from the evil of what I have done. I acknowledge Your favor upon me and I acknowledge my sin, so forgive me, for none forgives sins except You."
(Sahih al-Bukhari)
Hadith on Allah's Mercy
عَنْ أَبِي هُرَيْرَةَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: إِنَّ اللَّهَ يَبْسُطُ يَدَهُ بِاللَّيْلِ لِيَتُوبَ مُسِيءُ النَّهَارِ وَيَبْسُطُ يَدَهُ بِالنَّهَارِ لِيَتُوبَ مُسِيءُ اللَّيْلِ
An Abi Hurayrah Qala: Qala Rasulullahi sallallahu alayhi wasallam: Inna Allaha yabsutu yaddahu billayli liyatuba musee'u annahar, wayabsutu yadahu binnahar liyatuba musee'u allayl.
"Allah extends His Hand at night to accept the repentance of the one who sinned during the day, and He extends His Hand during the day to accept the repentance of the one who sinned during the night."
(Sahih Muslim)
Hadith on the Effect of Repentance
التَّائِبُ مِنَ الذَّنْبِ كَمَنْ لاَ ذَنْبَ لَهُ
At-ta'ibu min adh-dhanbi kaman la dhanba lahu.
"The one who repents from sin is like the one who never sinned."
(Sunan Ibn Majah)