All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The Witr prayer is a confirmed Sunnah. This is the preponderant opinion of the Muslim scholars. It is not an obligatory prayer like the other five obligatory prayers. Performing only one Rak’ah of Witr prayer is permissible. But despite its permissibility [of praying only one Rak’ah], praying three Rak’ahs, or five, or seven Rak’ahs is more perfect. The way of performing three Rak’ahs of Witr should not be similar to the way of performing the three Rak’ahs of Maghrib prayer. However, performing two Rak’ahs and concluding them with Tasleem and then praying one Rak’ah separately with a Tashahud and Tasleen is recommended.
Likewise, it is also allowed to pray three Rak’ahs consecutively without making Tashahud after the second Rak’ah, but the Tashahud should be in this case made only one time in the last Rak’ah, i.e. no Tashahud in the second Rak’ah as in Maghrib prayer.
The Witr prayer is like other supererogatory prayers, which may be performed while sitting or riding on any means of transport.
The evidence for the permissibility of praying only one Rak’ah of Witr is the Hadeeth reported by al-Bukhaari and Muslim that the Prophet said: "The prayer of the night is in sets of two Rak’ahs. If one fears the coming of the dawn, he should perform one Rak’ah, thereby making all of them odd (Witr)".
Imam Muslim adds after this narration that someone inquired Ibn ‘Umar about the meaning of 'sets of two Rak’ahs’, and he replied, after completing two Rak’ahs, finish them by Tasleem." This explanation of Ibn ‘Umar is also narrated from the Prophet Muhammad in al-Musnad.
There is a Hadeeth in which the Prophet said: “Witr is only one Rak’ah at the last part of the night.” [Muslim]
The Prophet also said: “Witr prayer is one's due; so whoever likes to perform five Rak'ahs of Witr, let him do so; whoever likes to perform three Rak'ahs of Witr, let him do so; whoever likes to perform one Rak'ah of Witr, let him do so. And whoever faces hardship to perform it, he may perform it only by making gestures.” [Abu Daawood, An-Nasaa’i, Ibn Maajah and Saheeh Ibn Hibbaan]
All the above Ahadeeth establish the fact that performing one Rak'ah of Witr prayer is permissible.
The evidence for the ruling that the three Rak'ahs of Witr should not be similar to the Maghrib prayer is the Hadeeth reported by Imam al-Haakim in his book entitled al-Mustadrak that the Prophet said: “Do not perform three Rak'ahs of Witr resembling to the Maghrib prayer. But you can perform five, or seven, or nine, or eleven Rakah of Witr, or more.”
The evidence that performing the Witr prayer while standing is not compulsory, is the Hadeeth narrated by Al-Bukhaari and Muslim that the Prophet sometimes performed Witr prayer while riding on his camel.
For more benefit on the Witr prayer, please refer to Fataawa 84482, 39577, 92197, 92752, 98754, 84999, and 351082.
Allah knows best.