Musnad Ahmad 30:3365

Yunus ibn Muhammad narrated to us, Hazm narrated to us, he said: I heard Muhammad ibn Wasi’, from some of his companions, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Whoever relieves a Muslim brother of a distress from the distresses of the world, Allah will relieve him of a distress from the distresses of the Hereafter. And whoever conceals [the faults of] his brother, Allah will conceal him in the world and the Hereafter. And Allah, the Almighty and Majestic, is in the aid of the servant as long as the servant is in the aid of his brother."