Musnad Ahmad 27:1196

Hajjaj narrated to us, Layth narrated to us, ‘Aqil narrated to me, from Ibn Shihab, that Salim ibn ‘Abdullah informed him, that ‘Abdullah ibn ‘Umar informed him, that the Messenger of Allah (may Allah bless him and grant him peace) said: "The Muslim is the brother of the Muslim; he does not wrong him, nor does he hand him over [to his enemy]. Whoever is in the need of his brother, Allah the Almighty and Majestic is in his need. Whoever relieves a Muslim of a distress, Allah the Almighty and Majestic will relieve him, by means of it, of a distress from the distresses of the Day of Resurrection. And whoever conceals [the faults of] a Muslim, Allah will conceal him on the Day of Resurrection."