Luke 23:48

And all the people that came together to that sight, beholding the things which were done, smote their breasts, and returned.

Cross-references

In Luke 23:34, Jesus prayed for forgiveness for the crucifiers; here the crowd's breast-beating shows their remorse.

Luke 18:13 uses the same phrase 'beat his breast' as a gesture of repentance, mirrored by the crowds here.