It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Do not give your property as ruqba; whoever is given something as ruqba, it belongs to the one to whom it was given."
And ruqba is that a man says: This is for so-and-so as long as he lives, and if so-and-so dies, it will belong to so-and-so (another person).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10954