Laudator Temporis Acti

Suetonius, Life of Augustus 40.3 (tr. Robert Graves):

Augustus thought it most important not to let the native Roman stock be tainted with foreign or servile blood, and was therefore very unwilling to create new Roman citizens or permit the manumission of more than a limited number of slaves. Once, when Tiberius requested that a Greek dependant of his should be granted the citizenship, Augustus wrote back that he could not assent unless the man put in a personal appearance and convinced him that he was worthy of the honour. When Livia made the same request for a Gaul from a tributary province, Augustus turned it down, saying that he would do no more than exempt the fellow from tribute — 'I would far rather forfeit whatever he may owe the imperial exchequer than cheapen the value of the Roman citizenship.'

magni praeterea existimans sincerum atque ab omni colluvione peregrini ac servilis sanguinis incorruptum servare populum, et civitates Romanas parcissime dedit et manumittendi modum terminavit. Tiberio pro cliente Graeco petenti rescripsit, non aliter se daturum, quam si praesens sibi persuasisset, quam iustas petendi causas haberet; et Liviae pro quodam tributario Gallo roganti civitatem negavit, immunitatem optulit affirmans facilius se passurum fisco detrahi aliquid, quam civitatis Romanae vulgari honorem.

See Clifford Ando, "Race and Citizenship in Roman Law and Administration," in Francisco Marco Simón et al, edd., Xenofobia y Racismo en el Mundo Antiguo (Barcelona: Edicions Universitat de Barcelona, 2019), pp. 175-188, who says at p. ?:

The most notorious racist in Roman history is surely the emperor Augustus.