Musnad Abu Ya'la al-Mawsili 111:61

Nasr ibn Ali ibn Nasr al-Jahdami narrated to us, Musa ibn al-Mughirah narrated to us, Abu Musa al-Saffar narrated to us, he said: I asked Ibn Abbas—or he was asked—which charity is best? He said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The best charity is water. Have you not heard of the people of the Fire when they sought help from the people of Paradise, saying: 'Pour upon us some water or from whatever Allah has provided you'?" (Al-A'raf: 50)