al-Husain bin Dhakwan al-Mua'lam الحسين بن ذكوان المعلم المكتب · The Book of Wills

"From Sufyan, from Az-Zuhri, from 'Ubaidullah bin 'Abdullah, from Ibn 'Abbas, that Sa'd bin 'Ubadah consulted the Prophet about a vow which his mother had to fulfill, but she died before doing so. The Messenger of Allah said: 'Fulfill it on her behalf.'"