Musannaf Ibn Abi Shaybah

Hazrat Dhahhak says that Witr is not obligatory upon a traveler.

Hazrat Abu Majliz narrates that I asked Hazrat Ibn Umar (may Allah be pleased with them both) about Witr: If I am in a state of travel, should I perform Witr? He replied: Perform one rak'ah at the end of the night.

Hazrat Khalid bin Dinar narrates from a Sheikh that I was on a journey with Hazrat Ibn Abbas (may Allah be pleased with them), and as far as I remember, he did not offer Witr.

Hazrat Saeed bin Jubair narrates that Hazrat Ibn Umar (may Allah be pleased with them) performed Witr during a journey.

Hazrat Ibn Umar (may Allah be pleased with both of them) and Hazrat Ibn Abbas (may Allah be pleased with both of them) state that offering Witr during travel is Sunnah.