Alhamdulillah, One of the most helpful and important ways of implementing Islam in our lives is to understand what we are encouraged to say and to realize the wisdom behind what we are commanded to act upon.
May Allah help us understand this Amazing religion of Islam in order to live accordingly, fulfill the purpose of our life and gain the ultimate success in both this life and the hereafter.
عن شداد بن أوس رضي الله عنه عن النبي صلى الله عليه وسلم قال: "سيد الإستغفار أن يقول العبد : اللهم أنت ربي، لا إله إلا أنت، خلقتني وأنا عبدك، وأنا على عهدك ووعدك ما استطعت أعوذ بك من شر ما صنعت أبوء لك بنعمتك علي، وأبوء بذنبي، فاغفر لي فإنه لا يغفر الذنوب إلا أنت، من قالها من النهار موقنا بها، فمات من يومه قبل أن يمسي، فهو من أهل الجنة، ومن قالها من الليل وهوموقن بها فمات قبل أن يصبح، فهو من أهل الجنة” (رواه البخاري).
Shaddad bin Aus (May Allah be pleased with him) said: The Prophet (ﷺ) said, "The best supplication for seeking forgiveness (Syed-ul- Istighfar) is to say: '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 bini'matika 'alayya, wa abu'u bidhanbi faghfir li, fa innahu la yaghfirudh-dhunuba illa Anta. (O Allah! You are my Rubb. There is no true god except You. You have created me, and I am Your slave, and I hold to Your Covenant as far as I can. I seek refuge in You from the evil of what I have done. I acknowledge the favours that You have bestowed upon me, and I confess my sins. Pardon me, for none but You has the power to pardon).' He who supplicates in these terms during the day with firm belief in it and dies on the same day (before the evening), he will be one of the dwellers of Jannah; and if anyone supplicates in these terms during the night with firm belief in it and dies before the morning, he will be one of the dwellers of Jannah." [Al-Bukhari].
عن ابن مسعود رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : "من قال: أستغفر الله الذي لا إله إلا هو الحي القيوم وأتوب إليه ، غفرت ذنوبه ، وإن كان قد فر من الزحف" (رواه أبو داود والترمذي والحاكم، وقال: حديث صحيح على شرط البخاري ومسلم).
Ibn Mas'ud (May Allah be pleased with him) said: The Messenger of Allah (ﷺ) said, "He who says: 'Astaghfir ullah-alladhi la ilaha illa Huwal-Haiyul-Qayyumu, wa atubu ilaihi (I seek the forgiveness of Allah, there is no true god except Allah, the Ever-Living, the Self- Subsisting, and I turn to Him in repentance),' his sins will be forgiven even if he should have run away from the battlefield (while he was engaged in fighting for the Cause of Allah)." [Abu Dawud, At-Tirmidhi and Al-Hakim (on conditions of Al-Bukhari and Muslim for accepting Hadith)].
Ibn al-Qayyim said in al-Wabil al-Sayyib (p. 77), when listing the benefits of dhikr (remembrance of Allah), including praying for forgiveness: Benefit no. 61: Dhikr gives a person strength so that he can do with dhikr that which he cannot do without it. I saw wonders in the strength of Shaykh al-Islam Ibn Taymiyah in walking, speech, courage and writing. He used to write in one day what a scribe would write in a week, or more. The troops saw his amazing strength in war. The Prophet (peace and blessings of Allah be upon him) taught his daughter Fatimah and ‘Ali (may Allah be pleased with them) to recite tasbeeh (glorification of Allah) thirty-three times every night when they went to bed, and to recite tahmeed (praises of Allah) thirty-three times, and to recite takbeer (magnification of Allah) thirty-four times, when she asked him for a servant and complained to him about the hardship of grinding corn, working and serving (her family). He taught her this and said: “It is better for you than a servant.” It was said: The one who persists in doing this will find strength in his body that will make him independent of the need for a servant. End quote.
With regard to the times for dhikr and the number of times it should be repeated, the believer should remember Allah at all times and in all situations. Allah says (interpretation of the meaning): “Those who remember Allah (always, and in prayers) standing, sitting, and lying down on their sides.” [Al ‘Imran 3:191]
The Prophet (peace and blessings of Allah be upon him) would remember Allah at all times. Narrated by Muslim.
So one should remember Allah a great deal and pray for forgiveness. The more he does that, the better.
Allah says (interpretation of the meaning): “O you who believe! Remember Allah with much remembrance.
And glorify His Praises morning and afternoon [the early morning (Fajr) and ‘Asr prayers].” [al-Ahzab 33:41, 42]
“... and the men and the women who remember Allah much with their hearts and tongues. Allah has prepared for them forgiveness and a great reward (i.e. Paradise).” [al-Ahzab 33:35].
Muslim (2702) narrated from al-Agharr al-Muzani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: “I ask Allah for forgiveness one hundred times a day.”
And Abu Dawood (1516) narrated that Ibn ‘Umar (may Allah be pleased with him) said: We used to count when the Messenger of Allah (peace and blessings of Allah be upon him) said in one sitting one hundred times: Rabb ighfir li wa tubb ‘alayya, innaka anta al-tawab al-raheem (Lord, forgive me and accept my repentance, for You are the Accepter of repentance, the Most Merciful). Classed as saheeh by al-Albani in Saheeh Abi Dawood.
حَدَّثَنَا صَدَقَةُ بْنُ الْفَضْلِ، أَخْبَرَنَا الْوَلِيدُ، عَنِ الأَوْزَاعِيِّ، قَالَ حَدَّثَنِي عُمَيْرُ بْنُ هَانِئٍ، قَالَ حَدَّثَنِي جُنَادَةُ بْنُ أَبِي أُمَيَّةَ، حَدَّثَنِي عُبَادَةُ بْنُ الصَّامِتِ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ "مَنْ تَعَارَّ مِنَ اللَّيْلِ فَقَالَ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ، لَهُ الْمُلْكُ، وَلَهُ الْحَمْدُ، وَهُوَ عَلَى كُلِّ شَىْءٍ قَدِيرٌ. الْحَمْدُ لِلَّهِ، وَسُبْحَانَ اللَّهِ، وَلاَ إِلَهَ إِلاَّ اللَّهُ، وَاللَّهُ أَكْبَرُ، وَلاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ. ثُمَّ قَالَ اللَّهُمَّ اغْفِرْ لِي. أَوْ دَعَا اسْتُجِيبَ، فَإِنْ تَوَضَّأَ وَصَلَّى قُبِلَتْ صَلاَتُهُ".
Narrated 'Ubada bin As-Samit: The Prophet (ﷺ) "Whoever gets up at night and says: -- 'La ilaha il-lallah Wahdahu la Sharika lahu Lahu-lmulk, waLahu-l-hamd wahuwa 'ala kullishai'in Qadir. Al hamdu lil-lahi wa subhanal-lahi wa la-ilaha il-lal-lah wa-l-lahu akbar wa la hawla Wala Quwata il-la-bil-lah.' (None has the right to be worshipped but Allah. He is the Only One and has no partners . For Him is the Kingdom and all the praises are due for Him. He is Omnipotent. All the praises are for Allah. All the glories are for Allah. And none has the right to be worshipped but Allah, And Allah is Great And there is neither Might nor Power Except with Allah). And then says: -- Allahumma, Ighfir li (O Allah! Forgive me). Or invokes (Allah), he will be responded to and if he performs ablution (and prays), his prayer will be accepted." Sahih al-Bukhari 1154.