عن أبي قتادة رضي الله عنه قال قال رسول الله صلى الله عليه وسلم خير ما يخلف الرجل من بعده ثلاث ولد صالح يدعو له وصدقة تجري يبلغه أجرها وعلم يعمل به من بعده رواه ابن ماجه بإسناد صحيح (الترغيب والترهيب 1/158)

Hazrat Abu Qataadah (radhiyallahu ‘anhu) reports that Rasulullah (sallallahu ‘alaihi wasallam) said, “The best things a person can leave behind after his demise are three; a pious child who makes du‘aa for him, sadaqah-e-jaariyah (the good that one leaves behind) the benefit and reward of which continues to reach one after his demise, and the knowledge of Deen (which he imparted to people) that people continue to practice after his demise.”