Musnad Ahmad 30:2777

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from ‘Abd al-Malik ibn ‘Umayr, from Abu Salamah, from Abu Hurayrah, from the Prophet, may God bless him and grant him peace, that he said: "Indeed, the truest line of poetry that the poets have spoken is: 'Behold, everything except God is vain.'"