’Ubaadah ibn as-Saamit radiallaahu ’anhu related that the Prophet sallallaahu ’alayhi wa sallam said:
“Whosoever seeks forgiveness for the believing men and the believing women, Allaah will record for that person – equivalent to every believing man and believing woman – a good deed.”
Related by al-Haythamî in Majma’az-Zuwaa‘id (l/210) where he said: “The isnaad is jayyid.”
[at-Tabarani, classed as Hasan by Al-Albani]
Supplications from the Noble Qur’aan:
“Our Lord! Forgive us and our brethren who have preceded us in Faith, and put not in our hearts any hatred against those who have believed. Our Lord! You are indeed full of kindness, Most Merciful. (Al-Hashr 59:10)
“Rabbana ighfir lana wali ikhwanina allatheena sabaqoona bi aleemani wala tajal fee quloobina ghillan lillatheena amanoo rabbana innaka raoofun raheemun
Wa ‘anaa ashhadu an laa ilaaha illal-laahu wahdahu laa shareeka lahu, wa ‘anna Muhammadan ‘abduhu wa Rasooluhu, radheetu billaahi Rabban, wa bi Muhammadin Rasoolan wabil-islami deenan.
‘I bear witness that none has the right to be worshipped but Allaah alone, Who has no partner, and that Muhammad is His Slave and His Messenger. I am pleased with Allah as my Lord, with Muhammad as my Messenger and with Islam as my religion.’
his sins would be forgiven 
[To be recited in Arabic after the Mu’aththin’s Tashahhud or the words of affirmation of faith]
“Whoever ate something, then said: الْحَمْـدُ للهِ الَّذي أَطْعَمَنـي هـذا وَرَزَقَنـيهِ مِنْ غَـيْرِ حَوْلٍ مِنِّي وَلا قُوَّة
Al-Hamdu lillaahilladhee at’amanee hadha wa razaqneeh min ghayri hawlin minnee wa la quwwa
‘Praise be to Allah who has fed me this food and provided it for me, without any strength or power on my part’
is forgiven his past and future sins.
“Whoever asks Allah sincerely for martyrdom [Allahumma inni as’aluk ash-shahadah], Allah will cause him to reach the status of the martyrs even if he dies in his bed.” [‘Sahih al-Bukhari’; # 1909]‘
[Al-`Adawee said it was sound, and that it was reported by by Muslim, page 55 of volume 13; Abu Dãwood, page 179 of volume 2; and Ibn Mãjah, #2797.]
‘And whosoever obeys Allaah and the Messenger then they will be in the company of those that Allaah has favoured: of the Prophets, the Truthful Ones (Siddeeq), the Martyrs and the Righteous – what an excellent company!’ (4:69).
The Messenger of Allaah -sallAllaahu alayhi wa sallam-said:
The supplication of Yunus, when he supplicated while he was in the belly of the whale: La ilaha ‘illa ‘anta, subhanaka ‘innee kuntu minath-thalimeena – There is none worthy of worship in truth except You, far are You from imperfection, indeed I am from amongst the Thalimoon (oppressors)
No Muslim ever supplicates with this for anything except that Allaah responds to him.
Listen to the Ayah :
Surah 21. (Verse 87). And (remember) Dhun-Nun, when he went off in anger, and imagined that We shall not punish him! But he cried through the darknesses (Zulumat) (saying): “There is none worthy of worship in truth except You, Glorified be You! Truly, I have been of the Zalimin wrongdoers.”)