Sunan an Nasai
3782
Sahih+2

It was narrated from 'Abdur-Rahman bin Samurah that the Messenger of Allah said:"If any one of you swears an oath, then he sees something better than it, let him offer expiation for his oath, and look at what is better and do it

SahihAbu Ghuddah
SahihAl-Albani