I spent a night with my maternal aunt Maymunah. The Prophet ﷺ got up to pray at night. He prayed thirteen rak'ahs including two rak'ahs of the dawn prayer. I guessed that he stood in every rak'ah as long as one could recite Surah al-Muzzammil (73).
بِتُّ عِنْدَ خَالَتِي مَيْمُونَةَ فَقَامَ النَّبِيُّ ﷺ يُصَلِّي مِنَ اللَّيْلِ فَصَلَّى ثَلاَثَ عَشْرَةَ رَكْعَةً مِنْهَا رَكْعَتَا الْفَجْرِ حَزَرْتُ قِيَامَهُ فِي كُلِّ رَكْعَةٍ بِقَدْرِ { يَا أَيُّهَا الْمُزَّمِّلُ } لَمْ يَقُلْ نُوحٌ مِنْهَا رَكْعَتَا الْفَجْرِ