Mishkat al-Masabih 254

Abu Huraira reported God’s messenger as saying, “Among the actions and good deeds for which a believer will continue to receive reward after his death are knowledge which he taught and spread, a good son whom he left behind, or a copy of the Qur'an which he left as a legacy, or a mosque which he built, or a house which he built for the traveller, or a stream which he caused to flow, or a sadaqa which he gave from his property when he was alive and well, for which he will continue to receive reward after his death.” Ibn Majah transmitted it, and also Baihaqi in Shu'ab al-iman.