Sayyiduna Jarir bin Abdullah (may Allah be pleased with him) said: "When the Prophet (peace and blessings be upon him) took a pledge of allegiance, he took it on bearing witness that there is no god worthy of worship except Allah and that Muhammad (peace and blessings be upon him) is the Messenger of Allah, and on establishing the prayer, paying the zakah, listening to and obeying Allah and His Messenger, and acting sincerely towards every Muslim."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2290