Pliny, Letters 3.5:
He managed all of this incredible work even among the middle of the labors and bustle of the city. In his retirement, he exempted only the time he spent in the bath from his studies. And when I say the bath, I mean the baths proper – for when he was being rubbed down or dried off, he was always either listening to some book or dictating. On the road, as though he were free from all other concerns, he left himself time for study alone: at his side was a secretary with a book and some tablets, whose hands were wrapped in gloves in the winter, so that not even the asperity of the weather could take away his study time. For this same reason, he was even carried in a chair at Rome. I remember one time that he hassled me for walking, and said, “You could have not wasted these hours,” because he thought that all time was wasted that was not spent in study. With this diligent application, he completed so many of those volumes of his, and left to me one hundred and sixty commentaries on selections, composed on both sides and in the minutest handwriting, which really doubled the number of volumes. He even used to say that when he was a procurator in Spain, he was able to sell these commentaries to Larcius Licinus for four hundred thousand coins; and at that time, he didn’t have so many of them to sell.
Haec inter medios labores urbisque fremitum. In secessu solum balinei tempus studiis eximebatur – cum dico balinei, de interioribus loquor; nam dum destringitur tergiturque, audiebat aliquid aut dictabat -.In itinere quasi solutus ceteris curis, huic uni vacabat: ad latus notarius cum libro et pugillaribus, cuius manus hieme manicis muniebantur, ut ne caeli quidem asperitas ullum studii tempus eriperet; qua ex causa Romae quoque sella vehebatur. Repeto me correptum ab eo, cur ambularem: ‘poteras’ inquit ‘has horas non perdere’; nam perire omne tempus arbitrabatur, quod studiis non impenderetur. Hac intentione tot ista volumina peregit electorumque commentarios centum sexaginta mihi reliquit, opisthographos quidem et minutissimis scriptos; qua ratione multiplicatur hic numerus. Referebat ipse potuisse se, cum procuraret in Hispania, vendere hos commentarios Larcio Licino quadringentis milibus nummum; et tunc aliquanto pauciores erant.