The Messenger of Allah ﷺ said, "By Allah, for one of you to persist stubbornly in an oath concerning his family is more sinful before Allah than for him to pay the expiation that Allah has prescribed."In another narration, "Whoever persists stubbornly in an oath concerning his family commits a greater sin than paying," meaning the expiation.
عن رسول الله ﷺ قال: والله لأن يلج أحدكم بيمينه في أهله، آثم له عند الله من أن يعطي كفارته التي فرض الله وفي رواية: من استلج في أهله بيمين فهو أعظم إثما ليبيريعني: الكفارة.
Bukhari narrated it in the Book of Oaths and Vows (6625), and Muslim narrated it in the Book of Oaths and Vows (1655), both from the hadith of Abdul-Razzaq, who said, Mamar narrated to us, from Hammam bin Munabbih, who said, "This is what Abu Hurairah narrated to us from the Messenger of Allah ﷺ," and he mentioned several hadiths, including this one, which he then related.As for the other narration, Bukhari narrated it (6626) from Ishaq bin Ibrahim, who said, Yahya bin Salih narrated to us, who said, Muawiya narrated to us, from Yahya, from Ikrima, from Abu Hurairah, and he related it.