Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
bayhaqi:15413Abū Naṣr b. Qatādah > Abū Manṣūr al-Naḍrawī > Aḥmad b. Najdah > Saʿīd b. Manṣūr > Jarīr > Manṣūr

[Machine] In His saying, "And it is not lawful for them to conceal what Allah has created in their wombs" [Surah Al-Baqarah 228], He said, "The majority of what is concerned with it is menstruation."  

البيهقي:١٥٤١٣أَخْبَرَنَا أَبُو نَصْرِ بْنُ قَتَادَةَ أنا أَبُو مَنْصُورٍ النَّضْرَوِيُّ نا أَحْمَدُ بْنُ نَجْدَةَ نا سَعِيدُ بْنُ مَنْصُورٍ نا جَرِيرٌ عَنْ مَنْصُورٍ عَنْ إِبْرَاهِيمَ

فِي قَوْلِهِ {وَلَا يَحِلُّ لَهُنَّ أَنْ يَكْتُمْنَ مَا خَلَقَ اللهُ فِي أَرْحَامِهِنَّ} [البقرة 228] قَالَ أَكْثَرُ مَا عُنِيَ بِهِ الْحَيْضُ