The Messenger of Allah ﷺ as saying: When a man dies, his action discontinues from him except three things, namely, perpetual sadaqah (charity), or the knowledge by which benefit is acquired, or a pious child who prays for him. (Using translation from Abū Dāʾūd 2880)
"إذَا ماتَ الإِنْسانُ انقطعَ عملُهُ إلَّا مِنْ ثلاثةٍ؛ إلا مِنْ صدقةٍ جاريةٍ، أو علمٍ يُنتفعُ به، أو ولدٍ صالحٍ يدْعُو لَهُ" .