Sahih al-Bukhari 57
Sahih al-Bukhari · Book 2: Belief · The statement of the Prophet (saws): Religion is An-Nasihah (to be sincere and true) to Allah, to His Messenger (Muhammad (saws)), to the Muslim rulers, and to all the Muslims
Narrated Jarir bin Abdullah:
حَدَّثَنَا مُسَدَّدٌ ، قَالَ حَدَّثَنَا يَحْيَى ، عَنْ إِسْمَاعِيلَ ، قَالَ حَدَّثَنِي قَيْسُ بْنُ أَبِي حَازِمٍ ، عَنْ جَرِيرِ بْنِ عَبْدِ اللَّهِ ، قَالَ بَايَعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم عَلَى إِقَامِ الصَّلاَةِ، وَإِيتَاءِ الزَّكَاةِ، وَالنُّصْحِ لِكُلِّ مُسْلِمٍ.
I gave the pledge of allegiance to Allah's Messenger (ﷺ) for the following: 1. offer prayers perfectly 2. pay the Zakat (obligatory charity) 3. and be sincere and true to every Muslim.