Surah Al-Baqarah 2:222

وَيَسْـَٔلُونَكَ عَنِ ٱلْمَحِيضِ ۖ قُلْ هُوَ أَذًى فَٱعْتَزِلُوا۟ ٱلنِّسَآءَ فِى ٱلْمَحِيضِ ۖ وَلَا تَقْرَبُوهُنَّ حَتَّىٰ يَطْهُرْنَ ۖ فَإِذَا تَطَهَّرْنَ فَأْتُوهُنَّ مِنْ حَيْثُ أَمَرَكُمُ ٱللَّهُ ۚ إِنَّ ٱللَّهَ يُحِبُّ ٱلتَّوَّٰبِينَ وَيُحِبُّ ٱلْمُتَطَهِّرِينَ

And they ask you about menstruation. Say, "It is harm, so keep away from wives during menstruation. And do not approach them until they are pure. And when they have purified themselves, then come to them from where Allāh has ordained for you. Indeed, Allāh loves those who are constantly repentant and loves those who purify themselves."

Translation: Saheeh International

Tafsir

They will ask you about the monthly period that is menstruation and the spot in which it occurs and how should one treat women during it. Say ‘It is an ailment filth or the place whence it issues is so; …

Excerpt from Tafsir al-Jalalayn, commentary on 2:222, via Quran.com. The reader has the full commentary and 9 more tafsirs.