The Gatehouse website record of a licence to crenellate for Raby Castle granted on 1378 May 10

Thomas, par la grace de Dieu, evesque de Duresme, a touz y qui cestez nos presentes lettres verront, ou orrount salutz. Sachez que nous de nostre grace chere especial et pour le grant amour que nous avons enver nostre chere et foial John de Nevill, Chivaler, Sieur de Raby, qui de long temps adeste de nostre consaill, et nous servant, lui eions grante et tant que nous est et licence especiall donc quil puisse de son manior de Raby, qe'st dedenz nostre roial seignurie dedans nostre Evechee de Duresme, faire un chastell fraunchement a sa volonte, et touz le tours, mesons, et mures, d'y celle, batailler et kirneller, sans estreent empescher molester–ou autres nos subjitz–ou demurant dedenz nostre did seignurie roial. A voir et tenir perpetuelement a lui et a ses heires issuit quil ne seoit pas prejudicial ne damagous a nous, ne a nostre eglise de Duresme, ne a noz successour en nule temps a venire. En temonaunce de quels choses, nous avons faitez faire cestez noz letters patentes. Don a Duresme par les meins Willielmi de Elmedon, nostre chauncellor, le disme jour de May, I'an. de nostre sacre trent et tierce.
Par lettre de private Seal.
Thomas, by the grace oh God, bishop of Durham, to all those who shall see or hear these our present letters: Know ye that we, of our dear and especial savor, and for the great love we bear to our dear and faithful John de Nevill, knight, lord of Raby, who has long been of our council and in our service, have granted, and as much as in us is do licence him freely, according to his will, to make a castle of his manor of Raby, which is within our royal lordship, and in our bishoprick of Durham; and all the towers, houses, and walls thereof, to embattle and crenellate without restraint, hindrance, or molestation––or other our subjests––or living within our royal lordship. To have and to hold to him and his heirs for ever, provided it shall not be prejudicial or injurious to us, our church at Durham, nor to our successors in time to come. In witness whereof, we have caused these our letters patent to be made. Given at Durham by the hands of William de Elmden our chancellor, on the 10th day of May, and in the 33d of our Consecration.
By writ of Privy Seal. (Grose)

Original source is;

1870, Report of the Deputy Keeper Public Records Vol. 32 p. 292

(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. Licentia is best translated as 'freedom to' not 'permission'.)

Significant later sources are;

Roy Martin Haines, ‘Hatfield, Thomas (c.1310–1381)’, Oxford Dictionary of National Biography, Oxford University Press, Sept 2004; online edn, Jan 2008 online copy (subscription may be needed)
Emery, Anthony, 1996, Greater Medieval Houses Vol. 1 (Cambridge) p. 159
King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol. 1 p. 141n16
Hodgson, J.F. 1880-9, Transactions of the Architectural and Archaeological Society of Durham and Northumberland Vol. 3 p. 123
Grose, Francis, 1787, The Antiquities of England and Wales (London) Vol. 2 p. 103-4 online copy

John Neville, fifth baron Neville (c. 1330-1388)

John Neville, fifth baron Neville (c. 1330-1388) Had long service with the crown as soldier and courtier. In his later years his service was mainly in the North particularly as warden of the eastern march and keeper of Bamburgh Castle. As an ally of John of Gaunt he maintained the balance of power in the north against the Percy family. His brother, Alexander Neville, was archbishop of York. This licence seems to be more to do with recognising the status of the Bishop of Durham (Hatfield had been a great politican and was still a very wealth man) and about the diplomatic moves to required to maintain co-operation between the great lords of the north of England.

Biographical source include;

Anthony Tuck, Sept 2004, ‘Neville, John, fifth Baron Neville (c.1330–1388)’ Oxford Dictionary of National Biography (Oxford University Press) online edn, Jan 2008 online copy (subscription may be needed)