وَأَقَلُّ الطُّهْرِ الْفَاصِلِ بَيْنَ الْحَيْضَتَيْنِ خَمْسَةَ عَشَرَ يَوْمًا، وَلَا حَدَّ لِأَكْثَرِهِ إِلَّا لِمَنْ بَلَغَتْ مُسْتَحَاضَةً
The minimum pure interval separating two distinct menstruations is 15 days. The matn gives no general maximum for Tuhr, while mentioning a special exception for a woman who reaches legal maturity while experiencing Istihadah; that advanced case is not expanded in this beginner level.