Abd al-Rahman bin Abi Rafi' narrates from his father (may Allah be pleased with him) that he was the slave of the daughter of the paternal uncle of Sayyiduna Umar bin al-Khattab (may Allah be pleased with him). She swore that her wealth was charity for the poor, so Sayyiduna Ibn Umar (may Allah be pleased with them both) said: "Expiate your oath."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20039