Musnad Ahmad 30:1636

'Abd al-Samad ibn 'Abd al-Warith narrated to us, Hammad narrated to us, from 'Ali ibn Zayd, from Abu al-Salt, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "I reached the seventh heaven and looked, and behold, above me were thunder and lightning bolts. Then I came upon a people whose bellies were like houses, in which were snakes that could be seen from the outside of their bellies. I said: 'Who are these?' He said: 'These are the consumers of usury.' When I descended and reached the lowest heaven, behold, there was dust, smoke, and voices. I said: 'Who are these?' He said: 'The devils, who hover over the eyes of the children of Adam, so that they do not reflect upon the kingdom of the heavens and the earth. And were it not for that, they would have seen wonders.'"