Diod. 38.4:

App. BC 1.74

Cic. deOrat. 3.9: For we ourselves remember, that Quintus Catulus, a man distinguished for almost every type of merit, when he entreated, not the security of his fortunes, but retreat into exile, was forced to deprive himself of life.
Cic. Brut. 4.307: In the same year Sulpicius lost his life; and Q. Catulus, M. Antonius, and C. Julius, three orators, who were partly contemporary with each other, were most inhumanly put to death.
Cic. Tusc. 5.56: Was not Marius happier, I pray you, when he shared the glory of the victory gained over the Cimbrians with his colleague Catulus (who was almost another Laelius, for I look upon the two men as very like one another,) than when, conqueror in the civil war, he in a passion answered the friends of Catulus, who were interceding for him, “Let him die” ? And this answer he gave, not once only, but often. But in such a case, he was happier who submitted to that barbarous decree than he who issued it. And it is better to receive an injury than to do one; and so it was better to advance a little to meet that death that was making its approaches, as Catulus did, than, like Marius, to sully the glory of six consulships, and disgrace his latter days, by the death of such a man.
Cic. Nat Deo 3.80-81: Why before that were so many leading citizens also made away with by Cinna? why had that monster of treachery Gaius Marius the power to order the death of that noblest of mankind, Quintus Catulus? The day would be too short if I desired to recount the good men visited by misfortune; and equally so were I to mention the wicked who have prospered exceedingly. For why did Marius die so happily in his own home, an old man and consul for the seventh time? why did that monster of cruelty Cinna lord it for so long? You will say that he was punished. It would have been better for him to be hindered and prevented from murdering so many eminent men, than finally to be punished in his turn.
Vell. 2.22.4: then there was Quintus Catulus, renowned for his virtues in general and for the glory, which he had shared with Marius, of having won the Cimbrian war; when he was being hunted down for death, he shut himself in a room that had lately been plastered with lime and sand; then he brought fire that it might cause a powerful vapour to issue from the plaster, and by breathing the poisonous air and then holding his breath he died a death according rather with his enemies’ wishes than with their judgement.
Val. Max. 9.12.4

Plut. Mar. 44
