Musnad Abu Ya'la al-Mawsili 117:216

Narrated to us Rawh ibn ‘Abd al-Mu’min, narrated to us ‘Ali ibn Abi Sarah, from Thabit, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A man from the people of Paradise will look down upon the people of Hellfire, and a man from the people of Hellfire will call out to him: 'O so-and-so, do you not recognize me?' He will say: 'No, by Allah, I do not recognize you. Woe to you, who are you?' He will say: 'I am the one who, when you passed by me in the world and asked me for a drink of water, I gave you to drink. So intercede for me with your Lord because of that.' He said: So that man entered upon Allah in His presence and said: 'O Lord, I looked down upon the people of Hellfire, and a man from the people of Hellfire stood up and called out: "O so-and-so, do you not recognize me?" I said: "No, by Allah, I do not recognize you. Who are you?" He said: "I am the one who, when you passed by me in the world and asked me for a drink, I gave you to drink. So intercede for me with your Lord because of that." O Lord, grant me intercession for him.' He said: So Allah will grant him intercession for him, and he will bring him out of the Hellfire."