Musnad Ahmad 30:446

Abu Kamil and 'Affan narrated to us, they said: Hammad narrated to us, from Suhayl. 'Affan said in his narration: Suhayl ibn Abi Salih informed us, from his father, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Hour will not be established until the people are rained upon with a rain from which the houses of mud-brick will not be protected, and from which only the houses of hair (tents) will be protected."