Sahih Bukhari Volume 3, Book 34, Hadith Number 366.

Narated By Jarir : I have given a pledge of allegiance to Allah’s Apostle for to testify that None has the right to be worshipped but Allah, and Muhammad is His Apostle, to offer prayers perfectly, to pay Zakat, to listen to and obey (Allah’s and His Prophet’s orders), and to give good advice to every Muslim.