Majma al-Zawaid 6943 — One who swears an oath and then sees something

Abd al-Rahman bin Udhaynah reports this statement of his father: The Prophet (peace and blessings be upon him) said: "Whoever swears an oath and then considers something else better than it, let him do what is better and give expiation for his oath."
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir; the narrator Abdullah bin Udhaynah is thiqah (trustworthy), and the rest of its narrators are the narrators of the Sahih. (At the beginning the narrator's name is given as Abd al-Rahman bin Udhaynah; perhaps this is a scribal error, or the narrator is someone else.)