Hazrat Abdullah Mughaffal (Radiallahu anhu) reports, "Sayyidina Rasulullah (Sallallahu alaihe wasallam) prohibited the combing of hair, but allowed it to be does occasionally."
Qazi Iyaz says that occasionally means after every three days. In Abu Daud a Hadith has been reported, wherein Sayyidina Rasulullah (Sallallahu alaihe wasallam) prohibited the combing of hair daily. The Ulama have written that it is prohibited at such times when there is no necessity for it, otherwise there is no harm in it. The prohibition is karahate tanzihi. It is specially for the hair that has no dirt in it and does not need grooming. When the hair is dirty, there is no karaaha (i.e. not makruh) in combing the hair daily.