ذِكْرُ مَا كَانَ يُطَوِّلُ ﷺ الرَّكْعَتَيْنِ الْأُولَيَيْنِ عَلَى اللَّتَيْنِ تَلِيَانِهِمَا مِنْ صَلَاةِ اللَّيْلِ بَعْدَ افْتِتَاحِهِ صَلَاةَ اللَّيْلِ بِرَكْعَتَيْنِ خَفِيفَتَيْنِ
I shall watch the prayer of the Messenger of Allah ﷺ at night. I slept at the threshold of his door or of his tent. The Messenger of Allah ﷺ prayed two light rak'ahs, and then prayed two long, long, long rak'ahs. He then prayed two rak'ahs that were not so long as the two rak'ahs before them ; he then prayed two rak'ahs that were less in duration, than the rak'ahs before them; again he prayed two rak'ahs that were less in length then the preceding rak'ahs; he then prayed two rak'ahs that were less in length than the previous rak'ahs. This made altogether thirteen rak'ahs. (Using translation from Abū Dāʾūd 1366)
أَنَّهُ قَالَ لَأَرْمُقَنَّ صَلَاةَ رَسُولِ اللَّهِ ﷺ اللَّيْلَةَ قَالَ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسْطَاطَهُ «فَقَامَ فَصَلَّى رَسُولُ اللَّهِ ﷺ رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَذَلِكَ ثَلَاثَ عَشْرَةَ رَكْعَةً»