Musnad Ahmad 30:265

Sufyan narrated to us, from Za'idah, from 'Abd al-Malik ibn 'Umayr, from Abu Salamah, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him: "The truest line of poetry a poet ever said is: 'Indeed, everything except Allah is false.' And Ibn Abi al-Salt almost became a Muslim."