Al-Nadr bin Anas said that Anas (may Allah be pleased with him) gave him half of his house as a gift. Abu Burdah said: "If you would like it to be valid for you, then take possession of it, for Umar bin al-Khattab (may Allah be pleased with him) ruled concerning gifts that whatever has been taken possession of is valid, and whatever has not been taken possession of is inheritance." Al-Nadr said: "So I called Yazid (al-Rishk), and he divided the house."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11959