Musannaf Ibn Abi Shaybah 38530 — the first to do a thing, and who did

Amir said that the first to pledge allegiance at the blessed hand of the Prophet (peace and blessings be upon him) beneath the tree, on the occasion of the Pledge of Ridwan, was Sayyiduna Abu Sinan bin Wahb al-Asadi (may Allah be pleased with him). The Messenger of Allah (peace and blessings be upon him) said to him: "On what are you pledging allegiance?" He replied: "On what is in your heart." So he pledged allegiance, and afterwards the other people also pledged allegiance at the blessed hand of the Prophet (peace and blessings be upon him).