Mujahid narrates from Sayyiduna Umar and Sayyidah Aishah (may Allah be pleased with them both) that they said: "(If) a man swears to walk (for Hajj), or that his wealth is charity for the poor, or that it is for the Ka'bah, then this is an oath; its expiation is feeding ten poor people."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20045