Surah An-Nur (The Light), Verse 28

فَاِنْ لَّمْ تَجِدُوْا فِیْهَاۤ اَحَدًا فَلَا تَدْخُلُوْهَا حَتّٰی یُؤْذَنَ لَكُمْ وَاِنْ قِیْلَ لَكُمُ ارْجِعُوْا فَارْجِعُوْا هُوَ اَزْكٰی لَكُمْ وَاللّٰهُ بِمَا تَعْمَلُوْنَ عَلِیْمٌ ۟

Fa il lam tajidoo feehaaa ahadan falaa tadkhuloohaa hattaa yu'zana lakum wa in qeela lakumurji'oo farji'oo huwa azkaa lakum; wallaahu bimaa ta'maloona 'Aleem

“If ye find no one in the house, enter not until permission is given to you: if ye are asked to go back, go back: that makes for greater purity for yourselves: and Allah knows well all that ye do.”

Quran 24:28 (Yusuf Ali Translation)