Musnad Ahmad 25:302

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Abu Bishr, who said: I heard Sa‘id ibn Jubayr narrating from Ibn ‘Abbas: That a woman vowed to perform Hajj, but she died. Her brother came to the Prophet, peace and blessings of Allah be upon him, and asked him about that. He said: "Do you see, if your sister had a debt, would you pay it off?" He said: "Yes." He said: "Then pay off [the debt owed to] Allah the Almighty and Majestic, for He is more deserving of fulfillment."