Qur'an 65:4

وَٱلَّـٰٓـِٔى يَئِسْنَ مِنَ ٱلْمَحِيضِ مِن نِّسَآئِكُمْ إِنِ ٱرْتَبْتُمْ فَعِدَّتُهُنَّ ثَلَـٰثَةُ أَشْهُرٍ وَٱلَّـٰٓـِٔى لَمْ يَحِضْنَ ۚ وَأُو۟لَـٰتُ ٱلْأَحْمَالِ أَجَلُهُنَّ أَن يَضَعْنَ حَمْلَهُنَّ ۚ وَمَن يَتَّقِ ٱللَّهَ يَجْعَل لَّهُۥ مِنْ أَمْرِهِۦ يُسْرًا

And for such of your women as despair of menstruation, if ye doubt, their period (of waiting) shall be three months, along with those who have it not. And for those with child, their period shall be till they bring forth their burden. And whosoever keepeth his duty to Allah, He maketh his course easy for him.