Praying Witr As One Rak’ah, By Ibn Hajar
Ibn Hajar said:
“It is authentically reported that a number of the Companions prayed one rak’ah for witr, without praying any nafl prior to it. It is recorded in Muhammad Ibn Nasr’s book and others, with an authentic isnaad from As-Saa’ib Ibn Yazeed, that ‘Uthmaan recited Quraan one night in just one rak’ah; and he did not pray anything else.
We will also cite in the chapter of Al-Maghaazee the report of ‘Abdullaah Ibn Tha’labah that Sa’d prayed one rak’ah for witr, and in al-Manaaqib the report that Mu’aawiyah prayed one rak’ah for witr, which was approved by Ibn ‘Abbaas.”
As for praying witr three rak’ah and giving salam after two, then standing up to pray the last rak’ah, then this was done by Ibn ‘Umar as is recorded in Saheeh Bukhari.