Mishkat al-Masabih 203
Abu Huraira reported God’s messenger as saying, “When a man 
dies no further reward is recorded for his actions, with three exceptions:
sadaqa which continues to be supplied, or knowledge from which benefit
continues to be reaped, or the prayers of a good son for his dead father.”
Muslim transmitted it.
وَعَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: " إِذَا مَاتَ الْإِنْسَانُ انْقَطَعَ عَمَلُهُ إِلَّا مِنْ ثَلَاثَةِ أَشْيَاءَ: صَدَقَةٍ جَارِيَةٍ أوعلم ينْتَفع بِهِ أوولد صَالح يَدْعُو لَهُ)
رَوَاهُ مُسلم