Musnad Ahmad 30:824

Yazid narrated to us, Hisham ibn Hassan informed us, from Muhammad ibn Wasi’, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever conceals his Muslim brother in the world, Allah will conceal him in the world and the Hereafter. And whoever relieves a distress from his brother from the distresses of the world, Allah will relieve from him a distress on the Day of Resurrection. And Allah is in the aid of the servant as long as the servant is in the aid of his brother."