Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that a woman came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah, my mother vowed to fast for a month, and she died before fasting. He (peace and blessings be upon him) said: "Tell me, if your mother had owed a debt, would you have paid it off?" She said: Yes. He (peace and blessings be upon him) said: "The debt of Allah is more deserving of being paid."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12312