As Salaam Alaykum Wa Rahmatullahi Wa Barakatuhu
Hair which we are forbidden to remove, which includes the eyebrows. The action of removing the hair of the eyebrows is called al-namas. It is also forbidden to remove the hair of the beard.
The evidence for that is the hadeeth of ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) who said:
I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: “Allaah has cursed the woman who does tattoos and the one who has them done, the woman who plucks eyebrows (al-naamisah) and the one who has it done (al-mutanammisah), and the one who files her teeth for the purpose of beauty, altering the creation of Allaah.”
Hair concerning which the texts are silent and do not say whether it is to be removed or left as it is, such as hair on the legs, hands, cheeks or forehead.
There is some difference of scholarly opinion concerning this.
Some said that it is not permissible to remove it, because removing it implies changing the creation of Allaah, as Allaah tells us that the Shaytaan said:
“ ‘and indeed I will order them to change the nature created by Allaah’”[al-Nisa’ 4:119 – interpretation of the meaning]
Some said that this is one of the things concerning which nothing was said, so the ruling is that it is allowed. It is permissible to leave it or to remove it, because whatever is not mentioned in the Qur’aan or Sunnah is permissible.
You can read to some others at this link:
http://www.islam-qa.com/en/ref/9037
http://www.islam-qa.com/en/ref/22393