It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "A bequest is not permissible for an heir, unless the heirs wish it."
This Ata is al-Khurasani; he did not meet Ibn Abbas and did not see him. Abu Dawud al-Sijistani and others said this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12534