All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It was narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Allaah Almighty curses those women who remove the hair of their eyebrows and do this for others and those who have this done for themselves…” The Prophet, sallallaahu ‘alayhi wa sallam, explained that the reason of prohibiting plucking eyebrows is the fact that it constitutes changing the creation of Allaah Almighty, as he said in the end of the Hadeeth: “…whereby they change the creation of Allaah Almighty.” The general indication of his statement “Allaah Almighty curses those women who remove the hair of their eyebrows…” includes whoever plucks the hair of the eyebrows, whether this is done to a little female child or an adult woman. If plucking eyebrows is prohibited for women—although they were allowed to use many means of adornment from which men are prohibited— then it is more logical and proper to judge that it is even more prohibited for men.
Therefore, it is prohibited for the guardian of a child or anyone to do that to him. Instead, his eyebrows should be left as they were created by Allaah Almighty, unless he needs to shave them for medical treatment or the like, in which case no sin is involved. If the cause no longer exists, then doing this becomes prohibited as it has been, following the rule which states that necessity must be answered proportionately.
Allaah Knows best.