Musnad Ahmad 25:1127

Yahya ibn Adam narrated to us, Isra'il narrated to us, from Simak, from 'Ikrimah, from Ibn 'Abbas, who said: "A group of the companions of the Prophet, peace and blessings of Allah be upon him, passed by a man from Banu Sulaym who had sheep with him. He greeted them with peace, so they said: 'He did not greet you with peace except to seek protection from you.' They then went to him and killed him, and took his sheep, and brought them to the Prophet, peace and blessings of Allah be upon him. Then Allah, Blessed and Exalted is He, revealed: 'And do not say to one who offers you [a greeting of] peace, "You are not a believer," aspiring for the goods of worldly life' [An-Nisa: 94], until the end of the verse."