Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Sayyiduna Sa'd bin Ubadah (may Allah be pleased with him) sought a ruling from the Prophet (peace and blessings be upon him) about a vow that was due from his mother, and she had died without fulfilling it. the Prophet (peace and blessings be upon him) said: "Fulfil it on her behalf."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5353