It is narrated from Hazrat Abu Huraira (may Allah be pleased with him) that Abu al-Qasim (peace and blessings be upon him) said: When any one of you insists on his oath regarding his family (even though it is wrong), then this is a greater sin in the sight of Allah than the expiation which has been prescribed for him.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 7743