Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Allah has approved three things for you and disapproved three things: He is pleased with you that you worship Him alone and do not associate partners with Him, that you hold firmly to the rope of Allah and do not split into sects, and that you be sincere to the ruler; and He has disliked for you gossip (qil wa qal), excessive questioning, and wasting wealth."
Ata' bin Yazid al-Laythi says: I heard Sayyiduna Tamim al-Dari (may Allah be pleased with him) saying that the Prophet (peace and blessings be upon him) said: "The religion is sincerity (nasihah)." He (peace and blessings be upon him) said this three times. It was asked: O Messenger of Allah! To whom? He said: "To Allah, to His Book, and to the leaders of the Muslims"; or he said: "to the leaders of the Muslims and their common people."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16656