Du'a for Tahajjud

اللَّهُمَّ لَكَ الْحَمْدُ أَنْتَ نُورُ السَّمَاوَاتِ وَالْأَرْضِ وَمَنْ فِيهِنَّ، وَلَكَ الْحَمْدُ أَنْتَ قَيِّمُ السَّمَاوَاتِ وَالْأَرْضِ وَمَنْ فِيهِنَّ، وَلَكَ الْحَمْدُ أَنْتَ الْحَقُّ، وَوَعْدُكَ الْحَقُّ، وَلِقَاؤُكَ حَقٌّ، وَقَوْلُكَ حَقٌّ، وَالْجَنَّةُ حَقٌّ، وَالنَّارُ حَقٌّ

Allahumma lakal-hamdu anta nurus-samawati wal-ardi wa man fihinn, wa lakal-hamdu anta qayyimus-samawati wal-ardi wa man fihinn, wa lakal-hamdu antal-haqq, wa wa'dukal-haqq, wa liqa'uka haqq, wa qawluka haqq, wal-jannatu haqq, wan-naru haqq.

“O Allah, to You belongs all praise — You are the Light of the heavens and the earth and whoever is in them. To You belongs all praise — You are the Sustainer of the heavens and the earth and whoever is in them. To You belongs all praise — You are the Truth, Your promise is true, the meeting with You is true, Your word is true, Paradise is true, and the Fire is true.”

The Prophet's ﷺ opening words when he stood for the night prayer.

Source: Bukhari 1120

اللَّهُمَّ لَكَ أَسْلَمْتُ، وَبِكَ آمَنْتُ، وَعَلَيْكَ تَوَكَّلْتُ، وَإِلَيْكَ أَنَبْتُ، وَبِكَ خَاصَمْتُ، وَإِلَيْكَ حَاكَمْتُ، فَاغْفِرْ لِي مَا قَدَّمْتُ وَمَا أَخَّرْتُ، وَمَا أَسْرَرْتُ وَمَا أَعْلَنْتُ

Allahumma laka aslamt, wa bika amant, wa 'alayka tawakkalt, wa ilayka anabt, wa bika khasamt, wa ilayka hakamt, faghfir li ma qaddamtu wa ma akhkhart, wa ma asrartu wa ma a'lant.

“O Allah, to You I have submitted, in You I have believed, upon You I have relied, to You I have turned, by You I have contended, and to You I have referred judgement. So forgive me what I have sent ahead and what I have left behind, what I have concealed and what I have declared.”

The continuation of the same du'a — the asking that follows the praise.

Source: Bukhari 1120