Musnad Ahmad 1017:32

Yahya ibn Sa'id narrated to us, from Sufyan, Alqamah ibn Marthad narrated to me, from Sulayman ibn Buraydah, from his father, that the Prophet (peace and blessings of Allah be upon him) prayed the prayers with one wudu on the day of the Conquest. Umar said to him: "You have done something you did not use to do." He said: "I did it intentionally."