Hadith: O Allah, to You I submit, in You I believe, upon You I rely, by Your help I contend with my foes, and to You I refer for judgment. So, forgive me the sins I committed in the past and those I may commit in the future, those I did secretly and those I did openly, and all that which You know of better than I do. There is no god but You

عن ابن عباس رضي الله عنهما كان النبيُّ صلى الله عليه وسلم إذا تَهَجَّد من الليل قال: «اللهم ربَّنا لك الحمدُ، أنت قَيِّمُ السموات والأرض، ولك الحمدُ أنت ربُّ السموات والأرض ومَن فيهنَّ، ولك الحمدُ أنت نورُ السموات والأرض ومن فيهنَّ، أنت الحقُّ، وقولُك الحقُّ، ووعدُك الحقُّ، ولقاؤك الحقُّ، والجنةُ حقٌّ، والنارُ حقٌّ، والساعةُ حقٌّ، اللهم لك أسلمتُ، وبك آمنتُ، وعليك توكَّلتُ، وإليك خاصمتُ، وبك حاكمتُ، فاغفر لي ما قدَّمتُ وما أخَّرتُ، وأسررتُ وأعلنتُ، وما أنت أعلم به مني، لا إلهَ إلا أنت».
[صحيح] - [متفق عليه]

Ibn ‘Abbās (may Allah be pleased with him) reported: When the Prophet (may Allah's peace and blessings be upon him) offered voluntary prayer during the night, he would say: "O Allah, our Lord! All praise belongs to You. You are the Custodian of the heavens and the earth, all praise belongs to You. You are the Lord of the heavens and the earth and all what is in them, all praise belongs to You. You are the Light of the heavens and the earth and all that is in them. You are the Truth, Your speech is the Truth, Your promise is the Truth, Your meeting is the Truth, Paradise is true, Hell-fire is true, and the Hour is true. O Allah, to You I submit, in You I believe, upon You I rely, By Your help I contend with my foes, and to You I refer for judgment. So, forgive me the sins I committed in the past and those I may commit in the future, those I did secretly and those I did openly, and all that which You know of better than I do. There is no god but You.”
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

When the Prophet (may Allah's peace and blessings be upon him) would rise during the night to offer voluntary prayer, after making the initial Takbīr to start the prayer, he would say, “O Allah, our Lord! All praise belongs to You”, i.e. all praise is due to Allah, the Exalted, for He is the One who is praised for His attributes, His names, His blessings, His favors, His creation, His actions, His commands, and His judgment. He is the One who is praised in the beginning and at the end, externally and internally. Then he said: “You are the Custodian of the heavens and the earth”, i.e. You are the One who brought them into existence from nothingness, the One who takes care of them with what will benefit them and maintain them. You are the Creator, the Provider, the Owner, the Manager, the Giver of life, and the Giver of death. Then he said: “All praise belongs to You, You are the Lord of the heavens and the earth and all that is in them”, i.e. You are their Owner and the owner of all that is in them, the Disposer of their affairs according to Your will. You brought them into existence from nothingness, so the kingdom belongs to You. No one other than You shares the dominion or manages the affairs, Blessed and Exalted You are. Then he said: “All praise belongs to You, You are the Light of the heavens and the earth and all that is in them”, i.e. one of His attributes is that He is light, and He concealed Himself from His creation by light. He, may He be glorified, illuminates the heavens and the earth, and is the Guide of the inhabitants of the heavens and the earth. It is not right to deny the attribute of light from Allah, Exalted, nor to interpret it. Then he said: “You are the Truth”, and the Truth is one of His names and attributes. He is the Truth in His essence and attributes. His existence is imperative, His attributes and characteristics are perfect. His existence is one of His inseparable attributes, and nothing exists except by Him. Then he said: “Your speech is the Truth”, i.e. all that You say is true, right and just. Falsehood cannot approach it from before it or from behind it. There is no falsehood in its reports, judgment, legislation, nor in its promise or warning. Then he said: “Your promise is the Truth”, i.e. You do not break the promise, so whatever You have promised must occur just as You promised it, neither broken nor changed. Then he said: “Your meeting is the Truth”, i.e. it is inevitable that the slaves will meet You and You will reward them for their deeds. The meeting includes seeing Allah, Glorified and Exalted. Then he said: “Paradise is true and Hell-fire is true”, i.e. both of them are established and existing, as You informed us that both of them are prepared for their inhabitants. They are the permanent abode and the final destination of the slaves. Then he said: “The Hour is true”, i.e. the coming of the Day of Judgment is a truth concerning which there is no doubt. It is established and must take place. It is the end of this world and the beginning of the Hereafter. His statement: “O Allah, to You I submit” means I surrender to Your judgment, yield to it and accept it. His statement: "in You I believe” means I have believed in You and what You sent down, and I have acted upon it. "Upon You I rely” means I have depended on You and entrusted my affairs to You. “By your help I contend with my foes” means I have used the proofs You brought to refute and defeat the one who is obstinate (in rejecting the truth). "To You I refer for judgment” means I have made You the Judge between me and anyone who refuses to accept the truth or opposes it, thereby refusing the judgment of all "Tāghūts" (i.e. false gods), such as man-made laws, soothsayers or anything from which mankind seeks a judgment, including principles which are baseless in the sight of the Islamic law. His statement: “So, forgive me the sins I committed in the past and those I may commit in the future, those I did secretly and those I did openly, and all that which You know of better than I do” means forgive all the sins that I have already committed and all the ones that I will commit; those that are apparent to anyone of Your creatures and those that are hidden from them, and those which no one knows of except You. Then he concluded his supplication with the statement: “There is no god but You”, therefore I do not turn towards anything except You. Anything worshiped other than You is false, and calling upon it is error and its consequence is evil. This is the pure monotheism that the messengers of Allah brought and it is what Allah has imposed upon His slaves.