Musnad Ahmad 790:130

Isma'il ibn Aban al-Warraq narrated to us, Abu Bakr al-Nahshali narrated to us, from Muhammad ibn al-Zubayr, from al-Hasan, from 'Imran ibn Husayn, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no vow in anger, and its expiation is the expiation of an oath."