In 1410, Ralph de Eure, knight ([Sir William Eure]) was granted, by Cardinal Langley, Bishop of Durham, (In year 5 of his reign) a Durham Pardon licence to crenellate Witton' (Witton Castle, Witton-le-Wear)

"Has pardon for enclosing and fortifying his manor of Witton' without licence, and permission to complete the same.
fortallicium"

the document is actually a pardon for unlicensed crenellation.

Original source is

• 1872, Report of the Deputy Keeper Public Records Vol33 p91

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms.)

Significant later source are;

• Emery, Anthony, 1996, Greater Medieval Houses Vol1 (Cambridge) p159
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol1 p141n18
  Bates, C.J., 1891, Border Holds of Northumberland (London and Newcastle: Andrew Reid) p. xv
  Hutchinson, Wm, 1785-94, The History and Antiquities of the County Palatine of Durham Vol3 p305, notes
  Grose, Francis, 1787, The Antiquities of England and Wales (London) Vol2 p112

More details about licences to crenellate can be found here.

Please let me know if you see any errors, can add information or can otherwise help to improve this resource. Contact me