Sunan An-Nasa'i

It was narrated from Sa'd bin 'Ubadah that his mother died. He said:""O Messenger of Allah, my mother has died; can I give charity on her behalf?"" He said: ""Yes."" He said: ""What kind of charity is best?"" He said: ""Providing drinking water."" And that is the drinking-fountain of Sa'd in Al-Madinah