Sunan Abu Dawud
772
Sahih+3

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

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid