Musannaf Ibn Abi Shayba 13:2679

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sa’id ibn Hassan narrated to us, he said: I heard Mujahid saying: "Whoever is granted a life-gift (*umra*), it is for him and for his heirs after him; it does not return to the one who granted it." And the *ruqba* (a form of conditional life-gift) is like it. I said to Mujahid: "What is the *ruqba*?" He said: "A man’s saying: 'It is for whichever of us two survives, me or you.'"