Musnad Ahmad 437:0

It was narrated from Maslamah ibn Mukhallad that the Messenger of Allah (ﷺ) said: "Whoever conceals the fault of a believer in this world, Allah will conceal his fault in this world and in the Hereafter. And whoever relieves a believer of a distress from the distresses of this world, Allah will relieve him of a distress from the distresses of the Day of Resurrection. And Allah remains in the aid of the servant as long as the servant is in the aid of his brother."