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!"
Related:
The Cow/2:167
"Those who follow will say: "If only we had had another chance, we would have shunned them as they now shun us". So Allah turns what they did into regret; they will not be able to come out of the Fire."
The Criterion/25:27
"On that Day the wrongdoer will bite his hand and say: "If only I had followed the same path with the Messenger"."
The Criterion/25:28
Woe to me, if only I had not taken so-and-so as a friend.
The Criterion/25:29
He led me astray from the message that reached me. Indeed, Satan leads a man astray.