Abdullah ibn Mas’ud reported: The Messenger of Allah, peace and blessings be upon him, said, “Allah did not send any Prophet to the nations before me but that he was given disciples and companions who held to his tradition and followed his command. Then, after them came their successors, who said what they did not practice and who practiced what they were not commanded. He who strove against them with his hand was a believer, and he who strove against them with his tongue was a believer, and he who strove against them with his heart was a believer; after that there is not even a mustard seed of faith.”
Source: Ṣaḥīḥ Muslim 50
Grade: Sahih (authentic) according to Muslim
عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ مَا مِنْ نَبِيٍّ بَعَثَهُ اللَّهُ فِي أُمَّةٍ قَبْلِي إِلَّا كَانَ لَهُ مِنْ أُمَّتِهِ حَوَارِيُّونَ وَأَصْحَابٌ يَأْخُذُونَ بِسُنَّتِهِ وَيَقْتَدُونَ بِأَمْرِهِ ثُمَّ إِنَّهَا تَخْلُفُ مِنْ بَعْدِهِمْ خُلُوفٌ يَقُولُونَ مَا لَا يَفْعَلُونَ وَيَفْعَلُونَ مَا لَا يُؤْمَرُونَ فَمَنْ جَاهَدَهُمْ بِيَدِهِ فَهُوَ مُؤْمِنٌ وَمَنْ جَاهَدَهُمْ بِلِسَانِهِ فَهُوَ مُؤْمِنٌ وَمَنْ جَاهَدَهُمْ بِقَلْبِهِ فَهُوَ مُؤْمِنٌ وَلَيْسَ وَرَاءَ ذَلِكَ مِنْ الْإِيمَانِ حَبَّةُ خَرْدَلٍ
50 صحيح مسلم كتاب الإيمان باب بيان أن النهي عن المنكر من الإيمان وأن الإيمان يزيد وينقص