Sayyiduna Jarir (may Allah be pleased with him) said: I pledged allegiance to the Messenger of Allah (peace and blessings be upon him) on establishing the prayer, paying the zakah, and acting sincerely towards every Muslim. (Al-Sha'bi said: And Jarir was perceptive.) I said: "O Messenger of Allah, as far as I am able."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2329