Musnad Ahmad 27:1472

Ishaq ibn Isa narrated to us, Malik informed me, from Abdullah ibn Dinar, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said to his companions: "Do not enter upon these people who are being punished, unless you are weeping. If you are not weeping, then do not enter upon them, lest there befall you the like of what befell them."