Sayyiduna Umar (may Allah be pleased with him) said: "A gift is inheritance as long as possession has not been taken."
It is narrated from Sayyiduna Uthman (may Allah be pleased with him), Ibn Umar and Ibn Abbas (may Allah be pleased with them) that charity (sadaqah) is not valid until possession is taken. Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) and Shurayh (may Allah have mercy on him) said: "Giving a gift is not valid until possession is taken."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11951