55. Before salam #1
Allah's Apostle (ﷺ) entered the mosque. Then a person is reciting Tashahhud towards the end of the prayer. He said -
اَللَّهُمَّ إِنِّي أَسْأَلُكَ يَا اللَّهُ بِأَنَّكَ الْوَاحِدُ الْأَحَدُ الصَّمَدُ الَّذِي لَمْ يَلِدْ وَلَمْ يُولَدْ وَلَمْ يَكُنْ لَهُ كُفُوًا أَحَدٌ أَنْ تَغْفِرَ لِي ذُنُوبِي إِنَّكَ أَنْتَ الْغَفُورُ الرَّحِيمُ
Allaahumma inni as'aluka ya Allahu bi annakal Wahidul-Ahad us-Samadulla-dhi lam yalid wa lam yowlad, wa lam yakun lahu kufuwan ahad, an taghfirali dhunubi, innaka antal-Ghafurur-Rahim
O Allah, I ask of You, O Allah, as You are the One, the Only, the Self-Sufficient Master, Who begets not nor was He begotten, and there is None equal or comparable to Him, forgive me my sins, for You are the Oft-Forgiving, Most Merciful.
The Messenger of Allah (ﷺ) said: "He has been forgiven," three times.
Related Duas:
When the rooster crows
Before salam #2
After awaking at night, reciting some specific duas
Dua of Lailatul Qadr
Dua for one who afflicted by a calamity
Dua at the time between Adhan and Iqamah
Dua when drinking Zamzam water with pure intention
Dua in the state of prostration
Dua after every obligatory prayer
Time when duas are accepted #1
While reciting Surah Fatiha behind the Imam
Dua after getting up from the rukoo