Sahih Bukhari
Oaths and Vows
Volume: 008 / Book Number: 078 / Hadith Number: 622
Narrated Abu Huraira:
Allah's Apostle said, "Anyone who takes an oath through which his family may be harmed, and insists on keeping it, he surely commits a sin greater (than that of dissolving his oath). He should rather compensate for that oath by making expiation."