Offering two optional rak’ahs after Witr.
Shaykh Al-Albani said in his book, Qiyam Ramadan:
One may offer two rak’ah voluntary prayer after witr prayer because they are affirmed by the action of the Prophet. Rather, he commanded his Ummah with it, saying:
آن هذا السفر جهد و ثقل، فإذا أوتر أحدكم فليركع ركعتين، فان استيقظ و الا كانت له
“This journey is strenuous and exhausting. If you pray witr, offer two rak’ah afterwards if you wake up, otherwise they will be written for you” (Reported by Ibn Khuzaimah in his Saheeh, ad-Daarimi and others, it is verified in as-Saheeha)
Regarding the hadith in which the Prophet (sallAllaahu ‘alayhi wa sallam) said:
اجعلوا آخر صلاتكم بالليل وترا
“Make your last prayer of the night Witr.” (Muslim)
The command in this hadith serves as an option and not an obligation.
The Sunnah is to recite Surah Zalzalah and Surah Al-Kafiroon in these two rak’ahs