On the authority of Tameem ibn Aus ad-Daree (may Allah be pleased with him):

The Prophet (peace and blessings of Allah be upon him) said, “The deen (religion) is naseehah (advice, sincerity).” We said “To whom?” He (peace and blessings of Allah be upon him) 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 و سلم قَالَ: "الدِّينُ النَّصِيحَةُ. قُلْنَا: لِمَنْ؟ قَالَ لِلَّهِ، وَلِكِتَابِهِ، وَلِرَسُولِهِ، وَلِأَئِمَّةِ الْمُسْلِمِينَ وَعَامَّتِهِمْ" .

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