Musnad Ahmad 1302:4

Muhammad ibn Ja'far and Hajjaj narrated to us, they said: Shu'bah narrated to us, from Qatadah. Hajjaj said in his narration: I heard Salim ibn Abi al-Ja'd narrating from Ma'dan, from Abu al-Darda', from the Prophet, may God bless him and grant him peace, that he said: "Whoever reads ten verses from the end of al-Kahf is protected from the trial of the Dajjal." Hajjaj said: "Whoever reads the last ten [verses] of Surat al-Kahf."