He who introduced some good practice in Islam which was followed after him (by people) he would be assured of reward like one who followed it, without their rewards being diminished in any respect. And he who introduced some evil practice in Islam which had been followed subsequently (by others), he would be required to bear the burden like that of one who followed this (evil practice) without their's being diminished in any respect.

جَاءَ نَاسٌ مِنَ الأَعْرَابِ إِلَى رَسُولِ اللَّهِ ﷺ عَلَيْهِمُ الصُّوفُ فَرَأَى سُوءَ حَالِهِمْ قَدْ أَصَابَتْهُمْ حَاجَةٌ فَحَثَّ النَّاسَ عَلَى الصَّدَقَةِ فَأَبْطَئُوا عَنْهُ حَتَّى رُئِيَ ذَلِكَ فِي وَجْهِهِ قَالَ ثُمَّ إِنَّ رَجُلاً مِنَ الأَنْصَارِ جَاءَ بِصُرَّةٍ مِنْ وَرِقٍ ثُمَّ جَاءَ آخَرُ ثُمَّ تَتَابَعُوا حَتَّى عُرِفَ السُّرُورُ فِي وَجْهِهِ فَقَالَ رَسُولُ اللَّهِ ﷺ مَنْ سَنَّ فِي الإِسْلاَمِ سُنَّةً حَسَنَةً فَعُمِلَ بِهَا بَعْدَهُ كُتِبَ لَهُ مِثْلُ أَجْرِ مَنْ عَمِلَ بِهَا وَلاَ يَنْقُصُ مِنْ أُجُورِهِمْ شَىْءٌ وَمَنْ سَنَّ فِي الإِسْلاَمِ سُنَّةً سَيِّئَةً فَعُمِلَ بِهَا بَعْدَهُ كُتِبَ عَلَيْهِ مِثْلُ وِزْرِ مَنْ عَمِلَ بِهَا وَلاَ يَنْقُصُ مِنْ أَوْزَارِهِمْ شَىْءٌ

Jarir reported that Messenger of Allah ﷺ delivered an address in which he exhorted people to give charity.

خَطَبَ رَسُولُ اللَّهِ ﷺ فَحَثَّ عَلَى الصَّدَقَةِ بِمَعْنَى حَدِيثِ جَرِيرٍ

The servant does not introduce good practice which is followed after him.... The rest of the hadith is the same.

قَالَ رَسُولُ اللَّهِ ﷺ لاَ يَسُنُّ عَبْدٌ سُنَّةً صَالِحَةً يُعْمَلُ بِهَا بَعْدَهُ ثُمَّ ذَكَرَ تَمَامَ الْحَدِيثِ

Jarir transmitted this hadith from his father through several other chains of narrators.

عَنِ النَّبِيِّ ﷺ ح وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ ح وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ حَدَّثَنَا أَبُو أُسَامَةَ ح وَحَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ حَدَّثَنَا أَبِي قَالُوا حَدَّثَنَا شُعْبَةُ عَنْ عَوْنِ بْنِ أَبِي جُحَيْفَةَ عَنِ الْمُنْذِرِ بْنِ جَرِيرٍ عَنْ أَبِيهِ عَنِ النَّبِيِّ ﷺ بِهَذَا الْحَدِيثِ

The Messenger of Allah ﷺ said: “Whoever calls to guidance will have a reward like the rewards of those who follow him, without that diminishing their rewards in the least. And whoever calls to misguidance will bear a sin like the sins of those who follow him, without that diminishing their sins in the least.”

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ: «مَنْ دَعَا إِلَى هُدًى كَانَ لَهُ مِنَ الأَجْرِ مِثْلُ أُجُورِ مَنْ تَبِعَهُ، لاَ يَنْقُصُ ذَلِكَ مِنْ أُجُورِهِمْ شَيْئًا، وَمَنْ دَعَا إِلَى ضَلاَلَةٍ كَانَ عَلَيْهِ مِنَ الإِثْمِ مِثْلُ آثَامِ مَنْ تَبِعَهُ، لاَ يَنْقُصُ ذَلِكَ مِنْ آثَامِهِمْ شَيْئًا».