I would definitely watch at night the prayer observed by the Messenger of Allah ﷺ. He prayed two short rak'ahs, then two long, long, long rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding, then he prayed two rak'ahs which were shorter than the two preceding, then observed a single one (Witr), making a total of thirteen rak'ahs  

أَنَّهُ قَالَ لأَرْمُقَنَّ صَلاَةَ رَسُولِ اللَّهِ ﷺ اللَّيْلَةَ فَصَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَذَلِكَ ثَلاَثَ عَشْرَةَ رَكْعَةً  

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.  

أَنَّهُ قَالَ لأَرْمُقَنَّ صَلاَةَ رَسُولِ اللَّهِ ﷺ اللَّيْلَةَ قَالَ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسْطَاطَهُ فَصَلَّى رَسُولُ اللَّهِ ﷺ رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَذَلِكَ ثَلاَثَ عَشْرَةَ رَكْعَةً  

“I said, I must observe how the Messenger of Allah ﷺ prays tonight. So I lay down at his door. The Messenger of Allah ﷺ got up and prayed two brief Rak’ah, then two long ones, which were very, very long, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah which were shorter than the ones preceding them, then two Rak’ah, then Witr. That was thirteen Rak’ah.”  

قُلْتُ لأَرْمُقَنَّ صَلاَةَ رَسُولِ اللَّهِ ﷺ اللَّيْلَةَ قَالَ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسْطَاطَهُ فَقَامَ رَسُولُ اللَّهِ ﷺ فَصَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ رَكْعَتَيْنِ ثُمَّ أَوْتَرَ فَتِلْكَ ثَلاَثَ عَشْرَةَ رَكْعَةً  

Yahya related to me from Malik from Abdullah ibn Abi Bakr from his father that Abdullah ibn Qays ibn Makhrama told him that Zayd ibn Khalid al-Juhani said one night that he was going to observe the prayer of the Messenger of Allah ﷺ. He said, "I rested my head on his threshold. The Messenger of Allah ﷺ got up and prayed two long, long, long rakas. Then he prayed two rakas which were slightly less long than the two before them. Then he prayed two rakas which were slightly less long than the two before them. Then he prayed two rakas which were slightly less long than the two before them. Then he prayed two rakas which were slightly less long than the two before them. Then he prayed two rakas which were slightly less long than the two before them. Then he prayed an odd raka, making thirteen rakas in all."  

أَنَّهُ قَالَ لأَرْمُقَنَّ اللَّيْلَةَ صَلاَةَ رَسُولِ اللَّهِ ﷺ قَالَ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسْطَاطَهُ فَقَامَ رَسُولُ اللَّهِ ﷺ فَصَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَتِلْكَ ثَلاَثَ عَشْرَةَ رَكْعَةً  

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»  

I would definitely watch at night the prayer observed by the Messenger of Allah ﷺ. He prayed two short rak'ahs, then two long, long, long rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding rak'ahs, then he prayed two rak'ahs which were shorter than the two preceding, then he prayed two rak'ahs which were shorter than the two preceding, then observed a single one (Witr), making a total of thirteen rak'ahs (Using translation from Muslim 765)  

أَنَّهُ قَالَ لَأَرْمُقَنَّ صَلَاةَ رَسُولِ اللهِ ﷺ «فَصَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَذَلِكَ ثَلَاثُ عَشْرَةِ رَكْعَةً»  

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 اللهِ ﷺ اللَّيْلَةَ قَالَ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسْطَاطَهُ فَصَلَّى رَسُولُ اللهِ ﷺ رَكْعَتَيْنِ خَفِيفَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ طَوِيلَتَيْنِ ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا ثُمَّ أَوْتَرَ فَتِلْكَ ثَلَاثَ عَشْرَةَ رَكْعَةً  

"عَنْ زَيْدِ بْنِ خَالِدٍ قَالَ: قُلْتُ: لأَرْمُقَنَّ (*) صَلَاةَ رسُولِ الله ﷺ فَتَوَسَّدْتُ عَتَبَتَهُ أَوْ فُسَطَاطَهُ، فَقَامَ رسُولُ الله ﷺ ، فَصَلَّى رَكْعَتَيْنِ خَفِيفَتَيْنِ، ثُمَّ صَلَّى رَكْعَتَيْنِ طَوِيلَتَيْنِ، ثُمَّ صَلَّى رَكَعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهَا، ثُمَّ صَلَّى رَكْعَتَيْنِ وَهُمَا دُونَ اللَّتَيْنِ قَبْلَهُمَا، ثم صلى ركعتين وهما دون اللتين قبلهمَا، ثم أَوْتَر، فَذَلِكَ ثَلَاثَ عَشْرَةَ رَكْعَةً".