What advice did the Prophet Muhammad (saw) give to Umar regarding the piece of land in Khaibar?
 Narrated Ibn `Umar:                     When `Umar got a piece of land in Khaibar, he came to the Prophet saying, "I have got a piece of land, better than which I have never got. So what do you advise me regarding it?" The Prophet said, "If you wish you can keep it as an endowment to be used for charitable purposes." So, `Umar gave the land in charity (i.e. as an endowments on the condition that the land would neither be sold nor given as a present, nor bequeathed, (and its yield) would be used for the poor, the kinsmen, the emancipation of slaves, Jihad, and for guests and travelers; and its administrator could eat in a reasonable just manner, and he also could feed his friends without intending to be wealthy by its means."