It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyiduna Sa'd bin Ubadah al-Ansari (may Allah be pleased with him) sought a ruling from the Messenger of Allah (peace and blessings be upon him) about a vow that was due from his mother, and she had died without fulfilling it. the Messenger of Allah (peace and blessings be upon him) said to him: "Fulfil it on her behalf." So the Muslims should follow this practice in everything that was due from a person who died without fulfilling it.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5348