Sahih Bukhari | Volume 9 | Hadith Number 418
Narrated by Ibn 'Abbas
A woman came to the Prophet and said, "My mother vowed to perform the Hajj but she died before performing it. Should I perform the Hajj on her behalf?" He said, "Yes! Perform the Hajj on her behalf. See, if your mother had been in debt, would you have paid her debt?" She said, "Yes." He said, "So you should pay what is for Him as Allah has more right that one should fulfill one's obligations to Him."