"I asked the Messenger Of Allah ﷺ about the unintentional glance, so he ordered me that I divert my sight."  

سَأَلْتُ رَسُولَ اللَّهِ ﷺ عَنْ نَظْرَةِ الْفَجْأَةِ فَأَمَرَنِي أَنْ أَصْرِفَ بَصَرِي  

from his father (from the Prophet ﷺ) who said: "O 'Ali! Do not follow a look with a look, the first is for you, but the next is not for you."  

يَا عَلِيُّ لاَ تُتْبِعِ النَّظْرَةَ النَّظْرَةَ فَإِنَّ لَكَ الأُولَى وَلَيْسَتْ لَكَ الآخِرَةُ