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 from Madinah to Makkah, though he (peace and blessings be upon him) feared no one but Allah, and would pray two rak'ahs at a time."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12803