Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Sayyiduna Sa'd bin Ubadah (may Allah be pleased with him) came to the Messenger of Allah (peace and blessings be upon him) and said: My mother has died, and a vow was due from her which she had not fulfilled. the Prophet (peace and blessings be upon him) said to him: "Fulfil it on her behalf."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5352