Sunan an-Nasai 18408
In-book no 3672أَخْبَرَنَا 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 ".
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.'"