Sunan an-Nasa'i, Hadith 3665 ⓘ
It was narrated that Sa'd bin 'Ubadah said: "I said: 'O Messenger of Allah, what kind of charity is best?' He said: 'Providing drinking water.'"
أَخْبَرَنَا أَبُو عَمَّارٍ الْحُسَيْنُ بْنُ حُرَيْثٍ، عَنْ وَكِيعٍ، عَنْ هِشَامٍ، عَنْ قَتَادَةَ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ سَعْدِ بْنِ عُبَادَةَ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ أَىُّ الصَّدَقَةِ أَفْضَلُ قَالَ " سَقْىُ الْمَاءِ " .
also referenced under: Book 30, Hadith 55 (In-Book) & Volume 4, Book 30, Hadith 3695 (DarusSalam)