From Sahih Bukhari (Hadith 1147):
Narrated Abu Salma bin `Abdur Rahman:I asked `Aisha, "How is the prayer of Allah's Messenger (ﷺ) during the month of Ramadan." She said, "Allah's Messenger (ﷺ) never exceeded eleven rak`at in Ramadan or in other months; he used to offer four rak`at-- do not ask me about their beauty and length, then four rak`at, do not ask me about their beauty and length, and then three rak`at." Aisha further said, "I said, 'O Allah's Messenger (ﷺ)! Do you sleep before offering the witr prayer?' He replied, 'O `Aisha! My eyes sleep but my heart remains awake
Reference: Bukhari 1147