Bukhari

Hadith Commentary:

Ibn Umar (radi Allahu anhuma), by narrating the incident of the Prophet (sallallahu alayhi wa sallam), in effect refuted his father, who had prohibited talbeed, whereas the Prophet (sallallahu alayhi wa sallam) himself performed talbeed. In any case, this was not the intention of Umar (radi Allahu anhu); rather, his intent was that one should not perform talbeed in a state other than ihram, thereby resembling those in ihram.

Hadith Commentary:
The position of Amir al-Mu’minin, Hazrat Umar radi Allahu anhu, was that a person who, while in the state of ihram, braids his hair to prevent it from becoming disheveled, should, upon completion (of the rites), have his head shaved rather than merely shortening the hair, just as one who performs talbeed (mats or plasters the hair) has his head shaved.
He likened the braiding of the hair to fixing it with gum or similar substances.
Hazrat Ibn Umar radi Allahu anhu understood from this that his esteemed father did not consider the act of talbeed to be preferable; therefore, he referred to the practice of the Messenger of Allah sallallahu alayhi wa sallam, stating that if the act of talbeed were not preferable, then why would the Messenger of Allah sallallahu alayhi wa sallam have practiced it?
(Fath al-Bari: 10/442)