Sayyiduna Abu Umamah (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Allah Almighty has given everyone who has a right his right. So a bequest is not permissible for an heir."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12537