Surah At-Talaq (The Divorce), Verse 4

وَاݨ یَىِٕسْنَ مِنَ الْمَحِیْضِ مِنْ نِّسَآىِٕكُمْ اِنِ ارْتَبْتُمْ فَعِدَّتُهُنَّ ثَلٰثَةُ اَشْهُرٍ وَّاݨ لَمْ یَحِضْنَ وَاُولَاتُ الْاَحْمَالِ اَجَلُهُنَّ اَنْ یَّضَعْنَ حَمْلَهُنَّ وَمَنْ یَّتَّقِ اللّٰهَ یَجْعَلْ لَّهٗ مِنْ اَمْرِهٖ یُسْرًا ۟

Wallaaa'ee ya'isna minal maheedi min nisaaa 'ikum inir tabtum fa'iddatuhunna salaasatu ashhurinw wallaaa'ee lam yahidn; wa ulaatul ahmaali ajaluhunna any yada'na hamlahun; wa many yattaqil laaha yaj'al lahoo min amrihee yusraa

“Such of your women as have passed the age of monthly courses, for them the prescribed period, if ye have any doubts, is three months, and for those who have no courses (it is the same): for those who carry (life within their wombs), their period is until they deliver their burdens: and for those who fear Allah, He will make their path easy.”

Quran 65:4 (Yusuf Ali Translation)