Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: "I prayed two rak'ahs while travelling with the Prophet (peace and blessings be upon him), and also with Sayyiduna Abu Bakr and Sayyiduna Umar (may Allah be pleased with them both)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9954