Musannaf Ibn Abi Shayba 7:452

Ibn ‘Uyaynah narrated to us, from al-Zuhri, from ‘Ubayd Allah, from Ibn ‘Abbas, that Sa‘d ibn ‘Ubadah asked the Prophet, peace and blessings of Allah be upon him, for a legal opinion regarding a vow that was upon his mother who had died before she could fulfill it. He said: "Fulfill it on her behalf."