Hadith 34:52
Abu Usama narrated to us, from Isma'il, [who] said: 'Amir informed us, [and] said: The first to pledge allegiance under the tree was Abu Sinan bin Wahb al-Asadi. The Messenger of Allah, peace and blessings of Allah be upon him, said to him: "Upon what do you pledge allegiance?" He said: "Upon what is in your soul." So he pledged allegiance to him, then the people followed successively and pledged allegiance to him.
حدثنا أبو أسامة عن إسماعيل أخبرنا عامر قال أول من بايع تحت الشجرة أبو سنان بن وهب الأسدي فقال له رسول الله صلى الله عليه وسلم علام تبايع قال على ما في نفسك فبايعه ثم تتابع الناس فبايعوه