On the authority of Tameem ibn Aus ad-Daree (ra):

The Prophet (ﷺ) said, “The deen (religion) is naseehah (advice, sincerity).” We said, “To whom?” He (ﷺ) said, “To Allah, His Book, His Messenger, and to the leaders of the Muslims and their common folk.” [Muslim]

عَنْ أَبِي رُقَيَّةَ تَمِيمِ بْنِ أَوْسٍ الدَّارِيِّ رَضِيَ اللهُ عَنْهُ أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ: "الدِّينُ النَّصِيحَةُ." قُلْنَا: لِمَنْ؟ قَالَ: "لِلَّهِ، وَلِكِتَابِهِ، وَلِرَسُولِهِ، وَلِأَئِمَّةِ الْمُسْلِمِينَ وَعَامَّتِهِمْ."

[رَوَاهُ مُسْلِمٌ]
Reference : 40 Hadith Nawawi 7
English translation : Hadith 7