From Sahih Bukhari (Hadith 1852):
Narrated Ibn `Abbas:A woman from the tribe of Juhaina came to the Prophet (ﷺ) and said, "My mother had vowed to perform Hajj but she died before performing it. May I perform Hajj on my mother's behalf?" The Prophet (ﷺ) replied, "Perform Hajj on her behalf. Had there been a debt on your mother, would you have paid it or not? So, pay Allah's debt as He has more right to be paid
Reference: Bukhari 1852