Sayyiduna Jarir (may Allah be pleased with him) said: "I pledged allegiance to the Messenger of Allah (peace and blessings be upon him) on testifying that there is no god worthy of worship except Allah and that Muhammad (peace and blessings be upon him) is His servant and Messenger, and on hearing and obeying, establishing the prayer, paying the zakah, and acting sincerely towards every Muslim."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2338