It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with him) that a man came to the Messenger of Allah (peace and blessings be upon him) and said: My sister vowed that she would perform Hajj, and she has died. He (peace and blessings be upon him) said: "If she had owed a debt, would you have paid it?" He said: Yes. He (peace and blessings be upon him) said: "Then pay what is due to Allah, for He is more entitled to it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12627