Ahadith on Tahajjud prayer done by Rasululllah.
'Ata Rahimahullah narrates that I asked 'Aishah Radiyallahu Anha:
Tell me the most unusual thing you have observed about Rasulullah SAW.
'Aishah replied: Was there anything in him that was unusual? One night he came to me and lay down in my blanket. Then he said: Leave me alone to worship my Rabb. After which he stood up, performed Wudu', and began to offer Solah and began to weep till his tears flowed down on his chest. Then he did Ruku' and after which he prostated and wept, then he raised his head and wept. He continued in this state until Bilal RA called him for Fajr Solah. I said: O Rasulullah! What made you weep, even though Allah has forgiven your past and future sins. He said: Should not then I be a grateful slave of Allah. And why should I not do so, when Allah has revealed these verses to me this night: Verily, in the creation of the heavens and the earth, and in the alternation of the night and the day, are signs for those who have knowledge (Quran surah Aal-Imran).
(Ibnu Hibban, Iqamatul Hujjah)
-Muntakhab AHadith (English version) Sunnah and Nafilah by Maulana Muhammad Yusuf