The Prophet ﷺ commanded to apply collyrium mixed with musk at the time of sleep. He said: A man who is fasting should abstain from it. Abu Dawud said: Yahya b. Ma'in said to me: This tradition about the use of collyrium is munkar (i.e. contradicts the sound traditions on the subject).  

عَنِ النَّبِيِّ ﷺ أَنَّهُ أَمَرَ بِالإِثْمِدِ الْمُرَوَّحِ عِنْدَ النَّوْمِ وَقَالَ لِيَتَّقِهِ الصَّائِمُ  

'Ubaid Allah b. Abu Bakr b. Anas reported on the authority of Anas b. Malik that he used to apply collyrium when he was fasting.  

أَنَّهُ كَانَ يَكْتَحِلُ وَهُوَ صَائِمٌ  

I did not see any of our companions who abominated the use of collyrium by a man who fasting. Ibrahim would permit the man who was fasting to apply collyrium with aloes.  

مَا رَأَيْتُ أَحَدًا مِنْ أَصْحَابِنَا يَكْرَهُ الْكَحْلَ لِلصَّائِمِ وَكَانَ إِبْرَاهِيمُ يُرَخِّصُ أَنْ يَكْتَحِلَ الصَّائِمُ بِالصَّبِرِ