Musnad Ahmad 30:3545

Rawh narrated to us, Hisham narrated to us, from Muhammad ibn Wasi’, from Muhammad ibn al-Munkadir, from Abu Salih, from Abu Hurayrah, that 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] a Muslim brother, Allah will conceal him in the world and the Hereafter. And Allah is in the aid of the servant as long as the servant is in the aid of his brother."