The religion is sincere counsel

On the authority of Abu Ruqayya Tamim ibn Aws ad-Dari (may Allah be pleased with him), that the Prophet (may Allah bless him and grant him peace) said three times: "The religion is sincerity.” We said: “To whom, O Messenger of Allah?” He said: “To Allah, to His Book, to His Messenger, to the leaders of the Muslims and to the Muslims at large."

Related by Muslim.

[Muslim 55]