Musnad Ahmad 1302:28

Rawh narrated to us, Sa'id narrated to us, from Qatadah, Salim ibn Abi al-Ja'd al-Ghatafani narrated to us, from Ma'dan ibn Abi Talhah al-Ya'mari, from Abu al-Darda', that the Prophet of Allah, peace and blessings of Allah be upon him, said: "Whoever memorizes ten verses from the beginning of Surat al-Kahf will be protected from the trial of the Dajjal."