Gaius, Commentaries on the Institutes of Civil Law 1.36-37

non tamen cuicumque volenti manumittere licet. nam is, qui in fraudem creditorum vel in fraudem patroni manumittit, nihil agit, quia lex Aelia Sentia inpedit libertatem.

However not everyone who wishes to free a slave is permitted to do so; for a man who frees a slave in order to defraud his creditors or his patron achieves nothing, because the lex Aelia Sentia prevents the grant of freedom.