It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that a woman came to the service of the Prophet (peace and blessings of Allah be upon him) and said: O Messenger of Allah (peace and blessings of Allah be upon him)! My mother has passed away, she had a month of fasts due, can I make them up on her behalf? The Prophet (peace and blessings of Allah be upon him) said: "Tell me, if your mother had a debt, would you pay it off or not?" She said: Of course. He said: "Then Allah's debt is more deserving of being paid."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 1970