(123) باب مَا يُسْتَفْتَحُ بِهِ الصَّلاَةُ مِنَ الدُّعَاءِ
Ibn 'Abbas said:
The Messenger of Allah (ﷺ) used to say in his tahajjud prayer(i.e. supererogatory prayer offered in or after the midnight) after he said the takbir; he then narrated the tradition to the same effect.
Reference: Sunan Abi Dawud 772
In-book reference: Book 2, Hadith 382
English translation: Book 2, Hadith 771