Prayer at Night (Tahajjud)

Bukhari :: Book 2 :: Volume 21 :: Hadith 249

Narrated 'Aisha:

I did not see the Prophet reciting (the Quran) in the night prayer while sitting except when he became old; when he used to recite while sitting, and when thirty or forty verses remained from the Sura, he would get up and recite them and then bow.