Sunan At-Tirmidhi

Abu An-Nadrah said:""Imran bin Husain was asked about the traveler's prayer. He said: 'I performed Hajj with the Messenger of Allah, and he prayed two Rak'ah. I performed Hajj with Abu Bakr, and he prayed two Rak'ah and with Umar, and he prayed two Rak;ah; and with Uthman for six years of his Khilafah, or eight years, and he prayed two Rak'ah