Surah al-Muzammil (The Enwrapped One) 73 : 4

Explantory Note 

Such is the preparation for the great task. It uses divine methods, which are guaranteed to succeed. The method is night worship, which on the higher level of remembrance of God takes up more than half the night but less than two-thirds, and on the lower level, but still in complete remembrance of Him, takes one-third of the night. This long time should be spent in prayer and recitation of the Qur'an, aloud but with calmness and without singing. It is authentically reported that the Prophet prayed his Witr in no more than 11 rak`ahs, but these took up nearly two-thirds of the night, and he read at length from the Qur'an.

"Sa’id ibn Hisham reports that he asked Ibn 'Abbas how the Prophet prayed Witr. He said: 'Shall I tell you who of all people knows this best?' He said: 'Yes.' Ibn 'Abbas said: 'Go and ask 'A'ishah and then come back and tell me her answer'." Sa’id continues: "I said to her: 'Mother of the believers, tell me what was the Prophet like in his manners?' She said: 'Do you not read the Qur'an?' I said I did. She said: 'His manners were as the Qur'an says.' I was about to leave, but then I thought of the Prophet's night worship, so I said: 'Mother of the believers, tell me how the Prophet offered his night worship.' She said: 'Do you not read the surah starting with, You enfolded one!' I said I did. She said: 'God made night worship obligatory at the opening of the surah, and the Prophet and his Companions offered night worship until their feet were swollen. God retained the end of that surah with Himself for 12 months, then the relaxation was given. Thus, night worship became voluntary after it had been obligatory.' I was about to rise, but then I remembered Witr, and I said to her: 'Mother of the believers, tell me how the Prophet offered Witr.' She said: 'We used to prepare for him his tooth stick and the water for his ablutions. He would rise at night, as God wished, and he would use his tooth stick to brush his teeth, then would perform his ablution. He would offer eight rak’ahs without sitting in between until he had completed the eighth rak’ah. He would then sit down and glorify God and supplicate, then he would stand before ending his prayer, to offer his ninth rak`ah. He would sit glorifying God alone, then supplicating. He would then finish his prayer with Salam. He said it aloud so that we would hear it. He then prayed two rak`ahs sitting down. Thus he would complete 11 rak’ahs. When he was older and put on some weight, he would pray Witr in seven rak`ahs and do two rak’ahs seated to complete nine. When the Prophet offered some voluntary prayers he liked to keep this up. If something distracted him from night worship, such as sleep or illness, he would offer 12 rak’ahs during the day. I know that the Prophet never read the whole of the Qur'an in one night up to the morning, and I know that he never fasted a complete month other than Ramadan'." [Related by Ahmad and Muslim.]