Sahih Muslim Book 25, Hadith 20
When a man dies, his acts come to an end, but three, recurring charity, or knowledge (by which people) benefit, or a pious son, who prays for him (for the deceased).
This hadith has been narrated on the authority of Hisham b. 'Urwa with the same chain of transmitters.
Umar acquired a land at Khaibar. He came to Allah's Apostle (ﷺ) and sought his advice in regard to it. He said: Allah's Messenger, I have acquired land in Khaibar. I have never acquired property more valuable for me than this, so what do you command me to do with it? Thereupon he (Allah's Apostle) said: If you like, you may keep the corpus intact and give its produce as Sadaqa. So 'Umar gave it as Sadaqa declaring that property must not be sold or inherited or given away as gift. And Umar devoted it to the poor, to the nearest kin, and to the emancipation of slaves, aired in the way of Allah and guests. There is no sin for one, who administers it if he eats something from it in a reasonable manner, or if he feeds his friends and does not hoard up goods (for himself). He (the narrator) said: I narrated this hadith to Muhammad, but as I reached the (words)" without hoarding (for himself) out of it." he (Muhammad' said:" without storing the property with a view to becoming rich." Ibn 'Aun said: He who read this book (pertaining to Waqf) informed me that in it (the words are)" without storing the property with a view to becoming rich."