Sahih Muslim 738 a
Abu Salama b. Abd al-Rahman asked 'A'isha about the (night) prayer of the Messenger of Allah (ﷺ) during the month of Ramadan. She said:
The Messenger of Allah (ﷺ) did not observe either in Ramadan or in other months more than eleven rak'ahs (of the night prayer). He (in the first instance) observed four rak'ahs. Ask not about their excellence and their length (i. e. these were matchless in perfection and length). He again observed four rak'ahs, and ask not about their excellence and their length. He would then observe three rak'ahs (of the Witr prayer). 'A'isha again said: I said: Messenger of Allah, do you sleep before observing the Witr prayer? He said: O 'A'isha, my eyes sleep but my heart does not sleep.
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ سَعِيدِ بْنِ أَبِي سَعِيدٍ الْمَقْبُرِيِّ، عَنْ أَبِي سَلَمَةَ بْنِ عَبْدِ الرَّحْمَنِ، أَنَّهُ سَأَلَ عَائِشَةَ كَيْفَ كَانَتْ صَلاَةُ رَسُولِ اللَّهِ صلى الله عليه وسلم فِي رَمَضَانَ قَالَتْ مَا كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَزِيدُ فِي رَمَضَانَ وَلاَ فِي غَيْرِهِ عَلَى إِحْدَى عَشْرَةَ رَكْعَةً يُصَلِّي أَرْبَعًا فَلاَ تَسْأَلْ عَنْ حُسْنِهِنَّ وَطُولِهِنَّ ثُمَّ يُصَلِّي أَرْبَعًا فَلاَ تَسْأَلْ عَنْ حُسْنِهِنَّ وَطُولِهِنَّ ثُمَّ يُصَلِّي ثَلاَثًا فَقَالَتْ عَائِشَةُ فَقُلْتُ يَا رَسُولَ اللَّهِ أَتَنَامُ قَبْلَ أَنْ تُوتِرَ فَقَالَ ‏
"‏ يَا عَائِشَةُ إِنَّ عَيْنَىَّ تَنَامَانِ وَلاَ يَنَامُ قَلْبِي ‏"‏ ‏.‏