Musannaf Ibn Abi Shayba 1:298

Waki’ narrated to us, from Sufyan, from Muharib ibn Dithar, from Ibn Buraydah, from his father, that he said: The Messenger of Allah (may Allah bless him and grant him peace) used to perform ablution for every prayer. When the day of the Conquest came, he prayed all the prayers with one ablution.