(8) باب فَضْلِ صَدَقَةِ الْمَاءِ
It was narrated that Sad bin Ubadah said:
"I said: 'O Messenger of Allah, what charity is best?' He said: 'Giving water to drink.'"
Reference: Sunan Ibn Majah 3684
In-book reference: Book 33, Hadith 28
English translation: Vol. 5, Book 33, Hadith 3684