The Ornaments of Gold - 43:38
"When he finally comes to Us, he says: "If only there had been between me and you a distance as far as the distance between two eastern countries, what an evil companion you have been!"
They do not realize that they serve Satan until the Day of Resurrection:
The Cattle/6:22
"On the Day when We gather them all together, We will say to those who associate partners, "Where are your partners whom you claim?"
The Cattle/6:23
"Their only defense will be: "By Allah our Lord, we did not associate partners."
The Heights/7:30
He guided a group to the right path and a group deserved to go astray. They have taken the devils as friends besides Allah, but they think that they are on the right path.
The Bee/16:28
"Those whom the angels take their lives while they are persecuting their souls. Then they surrender and say: "We were not doing any evil". Nay, Allah knows well what you do."