Al-Hasan (may Allah have mercy on him) reports from the Prophet (peace and blessings be upon him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever swears by a surah of the Qur'an owes an expiation for every verse; (then) if he wishes he may keep true (to his oath), and if he wishes he may break it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19898