After commencing the Tahajjud Salaah, recite the following duas before reciting Surah Faatihah:

Dua One

اَللّٰهُمَّ لَكَ الْحَمْدُ أَنْتَ قَيِّمُ السَّمٰوَاتِ وَالْأَرْضِ وَمَنْ فِيْهِنَّ وَلَكَ الْحَمْدُ لَكَ مُلْكُ السَّمٰوَاتِ وَالْأَرْضِ وَمَنْ فِيْهِنَّ وَلَكَ الْحَمْدُ اَنْتَ نُوْرُ السَّمٰوَاتِ وَالْأَرْضِ وَمَنْ فِيْهِنَّ وَلَكَ الْحَمْدُ أَنْتَ الْحَقُّ وَوَعْدُكَ الْحَقُّ وَلِقَاؤُكَ حَقٌّ وَقَوْلُكَ حَقٌّ وَالْجَنَّةُ حَقٌّ وَالنَّارُ حَقٌّ وَالنَّبِيُّوْنَ حَقٌّ وَمُحَمَّدٌ صَلّٰى اللهُ عَلَيْهِ وَسَلَّمَ حَقٌّ وَالسَّاعَةُ حَقٌّ اَللّٰهُمَّ لَكَ أَسْلَمْتُ وَبِكَ آمَنْتُ وَعَلَيْكَ تَوَكَّلْتُ وَإِلَيْكَ أَنَبْتُ وَبِكَ خَاصَمْتُ وَإِلَيْكَ حَاكَمْتُ فَاغْفِرْ لِيْ مَا قَدَّمْتُ وَمَا أَخَّرْتُ وَمَا أَسْرَرْتُ وَمَا أَعْلَنْتُ أَنْتَ الْمُقَدِّمُ وَأَنْتَ الْمُؤَخِّرُ لَا إِلٰهَ إِلَّا أَنْتَ وَلَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللّٰهِ

O Allah, all praise belongs to You and You are the Maintainer of the heavens and the earth and whoever is contained within them. All praise belongs to You and to You belongs the kingdom of the heavens and the earth and whoever is contained within them. All praise belongs to You and You are the noor (i.e. light) of the heavens and the earth and whoever is contained within them. You are Haqq, Your promises are true and Your meeting is true. Your speech is true, Jannah is true and Jahannum is true. The Ambiyaa (‘alaihimus salaam) are true and Hazrat Muhammad (sallallahu ‘alaihi wasallam) is true. The last hour is true. O Allah Ta‘ala, only to You have I surrendered. Only upon You have I brought Imaan. I have placed my trust and reliance only upon You. It is only towards You that I turn. It is only on account of You (i.e. with Your help) that I dispute (with the kuffaar in proving the truth). It is only towards You that I turn for judgement. Thus, forgive my sins - my past sins and my future sins, those sins commited in secret and those sins committed openly. You are the first and You are the last. There is none worthy of worship besides You, and there is no power (to do good) nor any ability (to abstain from evil) except with the help of Allah Ta‘ala. ^[1]