Musnad Ahmad 28:429

Nasr ibn Bab narrated to us, from Hajjaj, from ‘Amr ibn Shu‘ayb, from his father, from his grandfather, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) combined two prayers on the day he raided Banu al-Mustaliq." *** Al-Hakam ibn Musa narrated to us—‘Abdullah ibn Ahmad said: "And I heard it myself from al-Hakam ibn Musa"—Muslim ibn Khalid narrated to us, from Hisham ibn ‘Urwah, from his father, from ‘Abdullah ibn ‘Amr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever swears an oath, then sees something else that is better than it, let him do that which is better, and let him offer expiation for his oath."