Musannaf Ibn Abi Shayba 3:5832

Waki' narrated to us, he said: Ibn al-Mubarak narrated to us, from Yahya ibn Abi Kathir, from Muhammad ibn Abd al-Rahman ibn Thawban, he said: The Messenger of Allah (may Allah bless him and grant him peace) stayed in Tabuk for twenty nights, praying the prayer of the traveler as two rak'ahs.