It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) used to shorten the prayer while travelling between Madinah and Makkah, though he (peace and blessings be upon him) feared no one but Allah.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12799