John of Salisbury Letter Ex Insperato

A highly hagiographic letter, Ex Inspirato means unexpectedly.

In this letter John narrates the story of the murder of  Becket. It is the earliest written account which describes Becket's murder as a martyrdom. In this letter he refers to Becket as "the confessor of Christ" and "Christ's champion" and constantly stresses just how pious and righteous he had been. By emphasizing this piety John attempts to confirm that this murder truly was a martyrdom. And in the letter John asks whether he should be added to the lists of martyrs who should be venerated, but clarifying that this ultimately was a decision which the Pope would have to have the last word upon.

In this letter John of Salisbury tries to explain that it was almost inevitable that Becket would suffer much for receiving martyrdom from the hand of God, that though the murder was motivated by the Devil it had all yet been ordained by God. Becket would have known this since his return to England from exile that he would gain martyrdom, that he had received a sign from heaven about this, a sign from God which had announced to him his death. 

...
that you know of the passion of the glorious martyr Thomas, And because I did not doubt  the
Archbishop of Canterbury, who glorifies not only his own Church but every province of Eng-
land by his many great miracles.
...
And so for one of your learning to instruct our humble selves as to whether it would be safe
to invoke him as a guardian of salvation among the lists of the martyrs in the solemnities of
Masses and in other public prayers without the authority of the Roman Pontiff, or whether we
are bound to offer supplication prayers for him whom God has glorified by so many signs of
miracles, just as we would for any other departed soul.
...

Latin Version

John (of Salisbury, Bishop of Chartres): Edited J. Giles (1848). Joannis Saresberiensis Postea Epizcopi Carnotensis Opera Omnia ... Apud J. H. Parker. pp. 251–. 

Translation 

O'Connor, John Francis, "An Annotated Translation of the Letters of John of Salisbury" (1947). Master's Theses. Paper 672.
http://ecommons.luc.edu/luc_theses/672
Page 88-98
Letter 307/304
John of Salisbury to Bishop John Belmeis of Poitiers

References

Paul Dalton; Dr. Charles Insley; Louise J. Wilkinson (2011). Cathedrals, Communities and Conflict in the Anglo-Norman World. Boydell Press. pp. 170–. ISBN 978-1-84383-620-9.

Frank Barlow (1990). Thomas Becket. University of California Press. pp. 2–. ISBN 978-0-520-07175-9.

Actes Du Colloque International de Sedieres. Editions Beauchesne. pp. 78–.

Het Martelaarschap van Thomas Becket en Karel de Goede
by Sjoukje Telleman
Open Access version via Utrecht University Repository

William Duiker; Jackson Spielvogel (2012). World History, Volume I: To 1800. Murder in the Cathedral: Cengage Learning. pp. 376–. ISBN 1-133-71423-4.

H G Koenigsberger (2014). Medieval Europe 400 - 1500. Routledge. pp. 171–. ISBN 978-1-317-87089-0. 

What Became of the Bones of St Thomas?. CUP Archive. pp. 29–.