If any cohorts gave way in battle, he (Augustus) decimated them, and fed the rest on barley.
(Suetonius, Life of Augustus, 24.2)
More confirmation for the practice, not necessarily always in connection with decimatio:
Polybios: 6.37, Frontinus: Stratagems, 4.25/37, Plutarch: Antony 39, Plutarch: Marcellus 25.6, as well as Livius
27.13.9; Cassius Dio 49.27.1,...