Mansur narrates from al-Hasan (may Allah have mercy on him), and Hajjaj from Ata' (may Allah have mercy on him), that both of them said about a person who said that he would enter ihram for Hajj and then broke his oath: "He owes the expiation of an oath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20047