Sources

1) Source: Duchy of Lancaster: Deeds, Series LS "Confirmation by S[tephen v Langton], Archbishop of Canterbury, of the charter by Lewes Priory (Hugh, prior) to Humphrey de Bohun and Maud his mother concerning the election of priors of Farleigh, which charter Archbishop Hubert had also confirmed: (Wilts)". Dated: c1213-1215.. External Link
https://discovery.nationalarchives.gov.uk/details/r/C5414191. Reference: DL 27/4 (Data from direct source)
2) Source: Duchy of Lancaster: Deeds, Series L "Humphrey de Bohun the younger, son of Humphrey, Earl of Hereford and Essex"Dated: 1260 Evidence for Humphrey being father of Humphrey. This source can be tied specifically to this Humphrey as his son Humphrey is the only Humphrey who could be son of an Earl in 1265.. External Link
http://discovery.nationalarchives.gov.uk/details/r/C16101977. Reference: DL 25/3451/3002 (Data from direct source)
3) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I "Humphrey de Bohun, earl of Hereford and Essex...Humphrey, son of Humphrey de Bohun the younger, aged 24 and more, is his next heir."Dated: 1275 Evidences that Humphrey is father of Humphrey.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol2/pp65-72. Reference: C 133/8/9 (Data from direct source)
4) Source: English Baronies: a Study of Their Origin and Descent, 1086-1327. Reference: Pages 6-9: Barony of Miles of Gloucester (Questionable reliability of evidence)
5) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I "Humphrey de Bohun, earl of Hereford and Essex...Humphrey, son of Humphrey de Bohun the younger, aged 24 and more, is his next heir."Dated: 1275. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol2/pp65-72. Reference: C 133/8/9 (Data from secondary evidence)