It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both); he said: "The Messenger of Allah (peace and blessings be upon him) would travel between Makkah and Madinah fearing no one but Allah" (or he said: "dreading no one except Allah") and would pray two rak'ahs.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12802