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  

[Machine] A man from the Ansar came to the Prophet ﷺ with a handful of gold and said, "This is for the sake of Allah." Then Abu Bakr stood up and gave, and then Umar stood up and gave, and then the Muhajirun stood up and gave. And the face of the Messenger of Allah ﷺ brightened until I saw the radiance in his cheeks. Then he said, "Whoever starts a good practice in Islam and others act upon it, he will receive the reward of those who act upon it without their reward being diminished in any way. And whoever starts an evil practice in Islam and others act upon it, he will bear the burden of their sins without their sins being diminished in any way."  

أَنَّ رَجُلًا مِنَ الْأَنْصَارِ جَاءَ إِلَى النَّبِيِّ ﷺ بِصُرَّةٍ مِنْ ذَهَبٍ تَمْلَأُ مَا بَيْنَ أَصَابِعِهِ فَقَالَ هَذِهِ فِي سَبِيلِ اللهِ ﷻ ثُمَّ قَامَ أَبُو بَكْرٍ فَأَعْطَوْا فَأَعْطَى ثُمَّ قَامَ عُمَرُ فَأَعْطَى ثُمَّ قَامَ الْمُهَاجِرُونَ فَأَعْطَوْا قَالَ فَأَشْرَقَ وَجْهُ رَسُولِ اللهِ ﷺ حَتَّى رَأَيْتُ الْإِشْرَاقَ فِي وَجْنَتَيْهِ ثُمَّ قَالَ مَنْ سَنَّ سُنَّةً صَالِحَةً فِي الْإِسْلَامِ فَعُمِلَ بِهَا بَعْدَهُ كَانَ لَهُ مِثْلُ أُجُورِهِمْ مِنْ غَيْرِ أَنْ يُنْتَقَصَ مِنْ أُجُورِهِمْ شَيْءٌ وَمَنْ سَنَّ فِي الْإِسْلَامِ سُنَّةً سَيِّئَةً فَعُمِلَ بِهَا بَعْدَهُ كَانَ عَلَيْهِ مِثْلُ أَوْزَارِهِمْ مِنْ غَيْرِ أَنْ يُنْتَقَصَ مِنْ أَوْزَارِهِمْشَيْءٌ  

[Machine] The Prophet ﷺ once came across a group of Bedouins and noticed their poverty and hardship. He addressed the people, praised and glorified Allah, and then commanded them to give charity. He urged them and encouraged them to do so. They hesitated until the happiness could be seen in the face of the Messenger of Allah ﷺ . Then, a man came forward with a handful of leaves and gave it to him as charity. Another man followed and the people started giving charity one after another, until the happiness could be seen in the face of the Messenger of Allah ﷺ . He then said, "Whoever establishes a good practice in Islam, and it is acted upon after him, will receive its reward and the reward of those who act upon it without it detracting from their rewards. And whoever establishes an evil practice in Islam, and it is acted upon after him, will bear its burden and the burden of those who act upon it without it detracting from their burdens."  

أَتَى النَّبِيَّ ﷺ قَوْمٌ مِنَ الْأَعْرَابِ فَأَبْصَرَ عَلَيْهِمُ الْخَصَاصَةَ وَالْجَهْدَ فَخَطَبَ النَّاسَ فَحَمِدَ اللهَ ﷻ وَأَثْنَى عَلَيْهِ ثُمَّ أَمَرَهُمْ بِالصَّدَقَةِ وَحَضَّهُمْ عَلَيْهَا وَرَغَّبَهُمْ فِيهَا فَأَبْطَئُوا عَلَيْهِ حَتَّى رُؤِيَ ذَلِكَ فِي وَجْهِهِ فَجَاءَ رَجُلٌ بِقَبْضَةٍ مِنْ وَرِقٍ فَأَعْطَاهَا إِيَّاهُ ثُمَّ جَاءَ آخَرُ حَتَّى تَتَابَعَ النَّاسُ بِالصَّدَقَةِ حَتَّى رُؤِيَ فِي وَجْهِ رَسُولِ اللهِ ﷺ السُّرُورُ فَقَالَ «مَنْ سَنَّ فِي الْإِسْلَامِ سُنَّةً حَسَنَةً فَعُمِلَ بِهَا بَعْدَهُ كَانَ لَهُ أَجْرُهَا وَأَجْرُ مَنْ عَمِلَ بِهَا مِنْ غَيْرِ أَنْ يُنْتَقَصَ مِنْ أُجُورِهِمْ شَيْءٌ وَمَنْ سَنَّ فِي الْإِسْلَامِ سُنَّةً سَيِّئَةً فَعُمِلَ بِهَا مِنْ بَعْدِهِ كَانَ عَلَيْهِ وِزْرُهَا وَوِزْرُ مَنْ عَمِلَ بِهَا مِنْ غَيْرِ أَنْ يَنْقُصَ مِنْ أَوْزَارِهِمْ شَيْءٌ»