From Sahih Bukhari (Hadith 2013):
Narrated Abu Salama bin `Abdur Rahman:that he asked `Aisha "How was the prayer of Allah's Messenger (ﷺ) in Ramadan?" She replied, "He did not pray more than eleven rak`at in Ramadan or in any other month. He used to pray four rak`at ---- let alone their beauty and length----and then he would pray four ----let alone their beauty and length ---- and then he would pray three rak`at (witr)." She added, "I asked, 'O Allah's Messenger (ﷺ)! Do you sleep before praying the witr?' He replied, 'O `Aisha! My eyes sleep but my heart does not sleep
Reference: Bukhari 2013