Sayyiduna Ibn Umar (may Allah be pleased with them both) said: "The Messenger of Allah (peace and blessings be upon him) prayed two rak'ahs (while travelling), and so did Abu Bakr and Umar (may Allah be pleased with them both), and Uthman (may Allah be pleased with him) too during part of his caliphate (prayed two rak'ahs)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13203