حَدَّثَنَا مُحَمَّدُ بْنُ عَبَّادٍ الْمَكِّيُّ، حَدَّثَنَا سُفْيَانُ، قَالَ قُلْتُ لِسُهَيْلٍ إِنَّ عَمْرًا حَدَّثَنَا عَنِ الْقَعْقَاعِ، عَنْ أَبِيكَ، قَالَ وَرَجَوْتُ أَنْ يُسْقِطَ، عَنِّي رَجُلاً قَالَ فَقَالَ سَمِعْتُهُ مِنَ الَّذِي سَمِعَهُ مِنْهُ أَبِي كَانَ صَدِيقًا لَهُ بِالشَّامِ ثُمَّ حَدَّثَنَا سُفْيَانُ عَنْ سُهَيْلٍ عَنْ عَطَاءِ بْنِ يَزِيدَ عَنْ تَمِيمٍ الدَّارِيِّ أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏"‏ الدِّينُ النَّصِيحَةُ ‏"‏ قُلْنَا لِمَنْ قَالَ ‏"‏ لِلَّهِ وَلِكِتَابِهِ وَلِرَسُولِهِ وَلأَئِمَّةِ الْمُسْلِمِينَ وَعَامَّتِهِمْ ‏"‏ ‏.‏
Translation
It is narrated on the authority of Tamim ad-Dari that the Prophet (ﷺ) said

"The Religion is sincerity." We said, "To whom?" He said "To Allah, to His Book, To His Messenger, and to the leaders of the Muslims and their masses."

Comment

The Book of Faith - Sahih Muslim 55a

"The Religion is sincerity." We said, "To whom?" He said "To Allah, to His Book, To His Messenger, and to the leaders of the Muslims and their masses."

Commentary on Sincerity to Allah

Sincerity to Allah entails pure monotheism (tawhid), worshiping Him alone without partners, attributing to Him only what He has attributed to Himself in His Book and through His Messenger, and performing acts of worship solely for His pleasure.

Commentary on Sincerity to His Book

This requires believing in the Qur'an as the literal speech of Allah, uncreated, preserved from alteration, reciting it properly, implementing its rulings, and defending it against misinterpretation.

Commentary on Sincerity to His Messenger

This encompasses believing in Prophet Muhammad's message, following his Sunnah, loving him more than one's own self, reviving his teachings, and defending his honor and station.

Commentary on Sincerity to Muslim Leaders

This involves obeying them in what is right, advising them privately with wisdom, supporting them in establishing justice, and not rebelling against them unless they command clear disbelief.

Commentary on Sincerity to Muslim Masses

This includes guiding them to good, enjoining right and forbidding wrong, showing mercy to the young and respect to the elderly, and concealing their faults while advising them sincerely.