Sayyiduna Thawban (may Allah be pleased with him) narrates: We were traveling with the Prophet (peace and blessings of Allah be upon him). He said: "This journey is a cause of hardship and burden, so when a person performs Witr, he should also perform two rak'ahs. If he wakes up (at the time of Fajr prayer), then fine, otherwise these two will suffice for him."
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2577
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «الصحيحة» (1993).فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده قوي