Abdur-Rahman bin Thawban said: I heard 'Amr bin Deenar say: Someone who heard Ibn ‘Abbas (رضي الله عنه) told me that he said:

The Messenger of Allah (ﷺ) said: "Religion is sincerity (naseehah)." We said: To whom? He said: “To Allah, to His Messenger and to the leaders of the believers.”