Sahih Al Bukhari 1: Chapter 2, Hadith 57

(57) The statement of the Prophet : Religion is An-Nasihah (to be sincere and true) to Allah, to His Messenger (Muhammad ), to the Muslim rulers, and to all the Muslims

حَدَّثَنَا مُسَدَّدٌ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنَا يَحْيَى، ‏‏‏‏‏‏عَنْ إِسْمَاعِيلَ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ حَدَّثَنِي قَيْسُ بْنُ أَبِي حَازِمٍ، ‏‏‏‏‏‏عَنْ جَرِيرِ بْنِ عَبْدِ اللَّهِ، ‏‏‏‏‏‏قَالَ:‏‏‏‏ "بَايَعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَلَى إِقَامِ الصَّلَاةِ، ‏‏‏‏‏‏وَإِيتَاءِ الزَّكَاةِ، ‏‏‏‏‏‏وَالنُّصْحِ لِكُلِّ مُسْلِمٍ".

SAHIH HADITH:

Narrated Jarir bin Abdullah: I gave the pledge of allegiance to Allah's Apostle for the following: 1. offer prayers perfectly 2. pay the Zakat (obligatory charity) 3. and be sincere and true to every Muslim.

REFERENCE:

Sahih Al Bukhari 1: Chapter 2, Hadith 57