I have read in this Fatwa that; Shaving eyebrows is strictly forbidden since the Prophet (Sallallahu Alaihi wa Sallam) curse those who shave them. However, if the hair of eyebrows grow in an abnormal condition that deforms normal position of them then one may shave them only to remove the deformation.
1) Where has this information been taken from? Which Hadith? Is it authenticated?
I have read in a book - rules pertaining to Muslim women, which has also spoken of this. The source is; Majmu'al-Fataawa ash-Sheikh Muhammad Ibn Ibraheem (2/49). What is this source? A Hadith? Where has this information been taken from? I have real thick eyebrows that join, I have been threading for years, from the top, bottom and middle. What is defined as abnormal?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Al-Bukhari and Muslim reported from Ibn Masoud that he said: The Prophet (Sallallahu Alaihi wa Sallam) of Allah cursed those ladies who practice tattooing, those who get tattooed, those who cut the hair of their eyebrows, those who have their eyebrows hair cut and those who make up gaps between their teeth to get more beautiful changing thereupon the creation of Allah. this was reported to a woman from the tribe of Bani Asad called Um Yaqub , who went to Ibn Masoud , the narrator and said: What's the truth about a narration that was reported to me from you that you cursed those ladies who practise tattooing, …etc. Ibn Masoud replied: 'How can I (refrain from) not cursing someone the Prophet (Sallallahu Alaihi wa Sallam) cursed…. This is a sound Hadith reported by the most authentic books of al-Hadith: al-Bukhari and Muslim . Nevertheless, it is lawful for the woman to take from her eyebrows the hair that is disfiguring but not taking hair because it is too dense or not beautiful. In case, there is a removal of the deformation of the hair, it should be limited to the minimum necessary, not more. Allah knows best.