On the authority of Thawban (may Allah be pleased with him) that the Prophet (ﷺ) said:
إن هذا السفَرَ جَهْدٌ وثِقَلٌ، فإذا أَوْتَرَ أحدُكم فلْيَرْكَعْ ركعتين، فإن قام من الليلِ ؛ وإلَّا كانَتَا له
“Verily this journey is a struggle and burden, so when one of you prays witr, then let him offer two rak’aat [afterwards]. If he awakens [then he should pray them], and if not, then they are recorded for him”
[Graded Saheeh by al-Albani in Takhreej al-Mishkaat (no. 1238) and by Shaikh Muqbil in Saheeh Musnad (no. 190)]
The Prophet (ﷺ) himself used to pray these two rak’aat after witr:
أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يُصَلِّي بَعْدَ الْوِتْرِ رَكْعَتَيْنِ
“The Prophet (ﷺ) would pray two Rak’ah after Al-Witr.”
[Saheeh Tirmidhi no. 471]
Hafidh Ibn Rajab rahimahullah said:
“The Scholars differed about the two rak’aat after witr. Some of them recommended it and ordered it. From them is Kathir ibn Damrah and Khalid ibn Ma’daan. al-Hasan used to perform it sitting. It was mentioned previously that Abu Mijlaz used to perform it.
From our companions [i.e. the Hanaabilah] is the one who says that it is from the Sunnan ar-Raatibah. In the Hadith of Sa’d ibn Hishaam there is what proves that the Prophet (ﷺ) used to observe these two rak’aat.
From these [Scholars] is the one who said the two rak’aat after witr is the Sunnah for witr, like the Sunnah of maghrib after it. These two rak’aat do not remove maghrib from being the witr of the day due to the two rak’at after them.
From the Scholars is the one who allowed these two rak’aat and did not detest them. This is the statement of al-Awzaai’ and Ahmad. He [Ahmad] said: I hope that if he does it, he does not restrict it and he prays it sitting as comes in the Hadith. It was said to him: ‘Do you perform it”? He said: “no”.
Ibnul-Munthir said: “He did not dislike that”.
From these Scholars is the one who said that the Prophet (ﷺ) did that sometimes to clarify that it is allowed. And it was quoted from a group of Scholars that it is disliked. From them are Qays ibn Ubaadah, Malik, and Shafi’ee. As for Malik, then he did not know these two rak’aat after witr. Ibnul-Munthir mentioned that from him. As for Shafi’ee, it was quoted that he said the Prophet (ﷺ) ordered to make witr our last payer of the night, so we follow him in his (ﷺ) order. As for him doing so, then it was specific to him. Bayhaqi indicated that the Prophet (ﷺ) left off these two rak’aat and ended the matter by making witr the last prayer of his night. This indication towards the abrogation of the two rak’at is questionable”
Imam Ibn Qayyim rahimahullah said:
“What is correct is that it is said that these two rak’aat run the course of the Sunnah and the completion of the witr. For verily witr is a separate act of worship, especially if it is said it is obligatory. So these two rak’aat run the course of the Sunnah of maghrib for maghrib. For maghrib is the witr of the day and the two raka’aat after it complete it. Likewise the two rak’aat after witr of the night. And Allah Knows Best”
[Zad al-Ma’aad (1/321)]
Shaikh al-Albani rahimahullah said:
“I was hesitant regarding these two rak’aat for an extended time. So when I found this Noble Prophetic command, I hastened to hold on to it…”
[Qiyaaam ar-Ramadan (pg. 25)]
So these two rak’aat after witr are something legislated and from the Sunnah of the Prophet (ﷺ). It is Sunnah to recite surah al-Zilzal in the first rak’at of this prayer, followed by surah Kafiroon in the second as Shaikh al-Albani rahimahullah authenticated in Qiyaam ar-Ramadan (pg. 25) and Sifatus-Salah (pg. 140).
And Allah Knows Best
Faisal Ibn Abdul Qaadir Ibn Hassan