Surah No. 24, An Noor, Ayat No. 30

قُل لِّلْمُؤْمِنِينَ يَغُضُّوا مِنْ أَبْصَارِهِمْ وَيَحْفَظُوا فُرُوجَهُمْ ذَلِكَ أَزْكَى لَهُمْ إِنَّ اللَّهَ

o خَبِيرٌ بِمَا يَصْنَعُونَ

Translation :

(O Apostle) Say to the believing men, that they should lower their gaze (do not look at the forbidden things and beings) and guard their private parts : that will make greater purity for them: and Allah is well aware with all that they do.