Sahih Ibn Khuzaymah 2496 — 182 Subchapter: Virtue of giving water, if

Sayyiduna Sa’d (may Allah be pleased with him) narrates that I submitted, “O Messenger of Allah (peace be upon him), my mother has passed away. Should I give charity on her behalf?” The Prophet (peace be upon him) said, “Yes, do so.” I asked, “Which charity is best?” The Prophet (peace be upon him) said, “Providing water (i.e., have a well dug and dedicate it as a waqf).”