مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3024
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn ‘Abbas (رضي الله عنه) that Sa'd bin 'Ubadah asked The Messenger of Allah (ﷺ) about a vow that his mother had made but she died before she could fulfil it. The Messenger of Allah (ﷺ) said: "Fulfil it on her behalf."
Musnad Ahmad 3048A saheeh hadeeth]