I asked Messenger of Allah ﷺ about the sudden glance (that is cast) on the face (of a non-Mahram). He commanded me that I should turn away my eyes.  

سَأَلْتُ رَسُولَ اللَّهِ ﷺ عَنْ نَظَرِ الْفُجَاءَةِ فَأَمَرَنِي أَنْ أَصْرِفَ بَصَرِي  

This hadith has been narrated on the authority of Yunus through another chain of transmitters.  

عَنْ يُونُسَ بِهَذَا الإِسْنَادِ مِثْلَهُ