Musnad Ahmad 27:730

Yahya ibn Sa'id and Isma'il narrated to us, they said: Ibn 'Awn narrated to us, he said: Yahya said: Nafi' narrated to me, from Ibn 'Umar, that 'Umar said: "O Messenger of Allah, I have acquired land in Khaybar, and I have never acquired anything more precious to me than it." He said: "If you wish, you may withhold its essence and give its produce as charity." He said: So he gave it as charity, such that its essence is not sold, nor given away, nor inherited. He said: So he gave it as charity to the poor, the guest, the slaves, in the way of Allah, and the wayfarer. There is no blame upon the one who manages it if he eats from it in a reasonable manner or feeds a friend, without accumulating wealth from it.