Sayyiduna Awf bin Malik al-Ashja'i (may Allah be pleased with him) said: We were with the Messenger of Allah (peace and blessings be upon him), nine, eight or seven people. He (peace and blessings be upon him) said: "Will you not pledge allegiance to the Messenger of Allah (peace and blessings be upon him)?" We were new to pledging allegiance. We said: O Messenger of Allah, we have already pledged allegiance to you (peace and blessings be upon him). Then he (peace and blessings be upon him) said: "Will you not pledge allegiance to the Messenger of Allah (peace and blessings be upon him)?" We said: O Messenger of Allah, we have pledged allegiance. He (peace and blessings be upon him) said again: "Will you not pledge allegiance to the Messenger of Allah?" So we stretched out our hands and said: O Messenger of Allah, we have pledged allegiance to you (peace and blessings be upon him); on what shall we pledge allegiance? He (peace and blessings be upon him) said: "That you will worship Allah, not associate anything with Him, pray the five prayers, and obey." And he (peace and blessings be upon him) said one thing quietly: "And you will not ask people for anything." Indeed, if the whip of one of that group fell, he would not even ask anyone to hand it to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7874