Abd al-Rahman bin Abi Amrah al-Ansari (may Allah have mercy on him) reports from his mother (may Allah be pleased with her) that she intended to make a bequest, then postponed it until the morning; then she died, and she had intended to free a slave. Abd al-Rahman (may Allah have mercy on him) said to al-Qasim bin Muhammad (may Allah have mercy on him): If I free a slave on her behalf, will it benefit her? Al-Qasim (may Allah have mercy on him) said: Sa'd bin Ubadah (may Allah be pleased with him) said to the Messenger of Allah (peace and blessings be upon him): My mother has died; if I free a slave on her behalf, will it benefit her? The Messenger of Allah (peace and blessings be upon him) said: "Yes, free a slave on her behalf."
This is mursal (with a gap in the chain).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12638