Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "Do not make anything binding upon the 'aqilah (the kinsmen liable for blood money) on the basis of the statement of one who confesses."
Al-Tabarani recorded it. Its chain contains a narrator, al-Harith bin Nabhan, who is matruk (abandoned).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الديات / 10793