It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that once Sayyiduna Sa'd bin Ubadah (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) that his mother had made a vow, but she passed away before fulfilling it, so what is the ruling? The Prophet (peace and blessings be upon him) said: "You should fulfill it on her behalf."