Sunan an-Nasa'i, Volume 4, Book 30, Hadith 3694 (DarusSalam) ⓘ

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

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ الْمُبَارَكِ، قَالَ حَدَّثَنَا وَكِيعٌ، عَنْ هِشَامٍ، عَنْ قَتَادَةَ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ سَعْدِ بْنِ عُبَادَةَ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ إِنَّ أُمِّي مَاتَتْ أَفَأَتَصَدَّقُ عَنْهَا قَالَ ‏"‏ نَعَمْ ‏"‏‏.‏ قُلْتُ فَأَىُّ الصَّدَقَةِ أَفْضَلُ قَالَ ‏"‏ سَقْىُ الْمَاءِ ‏"‏‏.‏