Mukhtasar Bukhari

Narrated Ibn Abbas (may Allah be pleased with them) that a man came to the Prophet (peace and blessings of Allah be upon him) and said, "O Messenger of Allah! My mother has passed away and she had a month's fasts due. Should I fast on her behalf to make up for them?" The Prophet (peace be upon him) replied: "Yes, fulfilling Allah's debt is most deserving."