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.

Applying Kohl in the eye is Sunnah for both men and women.

The evidence about this is the saying of the Prophet (Sallallahu Alaihi wa Sallam): "If anybody amongst you applies Kohl (in his eye), he has to do that in odd numbers". [Reported by Ahmad and Al albani said that 'it is a sound Hadith']

The Prophet (Sallallahu Alaihi wa Sallam) also said: "Stick to applying the antimony, as it clarifies the sight and grows the eyelids". [Reported by Ibn Majah and Al albani graded it as sound]

Al-Munthiri in his book ‘Al Targheeb’ entitled a chapter: 'The chapter of encouraging men and women to apply Kohl'.

Ibn al-Qayyim had spoken about its importance in health and its excellence, so he mentioned the following as part of the guidance of the Prophet (Sallallahu Alaihi wa Sallam) in protecting the health of the eyes:

Abu Dawud reported in his Sunnah that the Prophet (Sallallahu Alaihi wa Sallam) ordered us to apply "The antimony which is moisturized by musk, when going to sleep”, and he said, “a fasting person should avoid it".

In Sunan Ibn Majah and others, Ibn Abbas, (Radiya Allahu Anhuma) said: "The Prophet (Sallallahu Alaihi wa Sallam) used to have a Kohl container and used to apply Kohl 3 times in each eye".

'Kohl protects the health of the eye and strengthens the sight.  Some kinds of Kohl add beauty to the eye, and when sleeping it has more benefit as the eye is still.  The antimony has that peculiarity about it.' [Zad Al-Miad, 4/280]

Many Ahadith were mentioned about the excellence of antimony.

In this regard it is sufficient to mention the Hadith reported by Ahmad, Abu Dawud, Ibn Majah and Ibn Hibban with a good chain of narration, that Ibn Abbas, (Radiya Allahu Anhu) and his father narrated that the Prophet (Sallallahu Alaihi wa Sallam) said: "The best of your Kohl is the antimony; it strengthens the sight and grows the eyelids".

Allah knows best.