From Sahih Muslim (Hadith 4291):
Hammam b. Munabbih reported:This is what Abu Huraira reported to us from Allah's Messenger (ﷺ), and he narrated a hadith and (one) of them is that Allah's Messenger (ﷺ) said: I swear by Allah, it is more sinful in Allah's sight for one of you to persist in an oath regarding his family than payment of its expiation which Allah has imposed upon him (for breaking the oath)
Reference: Muslim 4291