Ancient authors on the issue of the Varus Battle

Caius Suetonius Tranquillus, The Lives of the Twelve Caesars.
The life of Augustus 23.49

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23.

He suffered but two severe and ignominious defeats, those of Lollius and Varus, both of which were in Germany. Of these the former was more humiliating than serious, but the latter was almost fatal, since three legions were cut to pieces with their general, his lieutenants, and all the auxiliaries. When the news of this came, he ordered that watch be kept by night throughout the city, to prevent outbreak, and prolonged the terms of the governors of the provinces, that the allies might be held to their allegiance by experienced men with whom they were acquainted. He also vowed great games to Jupiter Optimus Maximus, in case the condition of the commonwealth should improve, a thing which had been done in the Cimbric and Marsic wars. In fact, they saw that he was so greatly affected that for several months in succession he cut neither his beard nor his hair, and sometimes he would dash his head against a door, crying: »Quintilius Varus, give me back my legions!« And he observed the day of the disaster each year as one of sorrow and mourning. 
 (…)
49.

Of his military forces he assigned legions and auxiliaries to the various provinces, (…) and employed the remainder partly in the defence of the city and partly in that of his own person, disbanding a troop of (…) Germans, which he had retained until the defeat of Varus. (…)

Caius Suetonius Tranquillus, The Lives of the Twelve Caesars.
The life of Tiberius  17-18

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17.

Circumstances gave this exploit a larger and crowning glory; for it was at just about that time that Quintilius Varus perished with three legions in Germany, and no one doubted that the victorious Germans would have united with the Pannonians, had not Illyricum been subdued first. Consequently a triumph was voted him and many high honours. (...) Tiberius himself put off the triumph, because the country was in mourning for the disaster to Varus (...)

18.

The next year he returned to Germany, and realising that the disaster to Varus was due to that general's rashness and lack of care, he took no step without the approval of a council; while he had always before been a man of independent judgment and self-reliance, then contrary to his habit he consulted with many advisers about the conduct of the campaign. (...)

This webpage reproduces a section of:
The Lives of the Twelve Caesars by C. Suetonius Tranquillus, published in the Loeb Classical Library, 1913; The English translation is by J. C. Rolfe, printed in the same edition: Harvard University Press