The reference to St Paul alludes to 2 Timothy iv, 2. The anecdote concerning Pyrrhus is narrated by Plutarch in his Life of Pyrrhus. Cicero discusses humour towards the end of the second book of the de Oratore and Quintilian in the Institutio oratoria (6, 3). Julius Caesar's willingness to forgive is remarked on by Suetonius in his Lives of the Caesars.