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.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
bayhaqi:1536 – Abū Bakr b. al-Ḥārith al-Faqīh > Abū Muḥammad ʿAbdullāh b. Muḥammad b. Jaʿfar b. Ḥibbān Abū al-Shaykh al-Aṣbahānī > Muḥammad b. Yaḥyá b. Mandah > Abū Saʿīd al-Ashaj > Ibn Idrīs > Mufaḍḍal b. Muhalhal > Sufyān al-Thawrī > Ibn Jurayj > ʿAṭāʾ

[Machine] The majority of menstruation lasts for fifteen days.  

البيهقي:١٥٣٦ – أَخْبَرَنَا أَبُو بَكْرِ بْنُ الْحَارِثِ الْفَقِيهِ أنا أَبُو مُحَمَّدٍ عَبْدُ اللهِ بْنِ مُحَمَّدِ بْنِ جَعْفَرِ بْنِ حِبَّانَ أَبُو الشَّيْخِ الْأَصْبَهَانِيُّ حَدَّثَنِي مُحَمَّدُ بْنُ يَحْيَى بْنِ مَنْدَهْ ثنا أَبُو سَعِيدٍ الْأَشَجُّ ثنا ابْنُ إِدْرِيسَ عَنْ مُفَضَّلِ بْنِ مُهَلْهَلٍ عَنْ سُفْيَانَ الثَّوْرِيِّ عَنِ ابْنِ جُرَيْجٍ عَنْ عَطَاءٍ قَالَ

أَكْثَرُ الْحَيْضِ خَمْسَةَ عَشَرَ يَوْمًا  

See similar narrations below:

Collected by Dārimī, Bayhaqī
bayhaqi:15407 – Abū Bakr b. al-Ḥārith > ʿAlī b. ʿUmar al-Ḥāfiẓ > Ibrāhīm b. Ḥammād > Muḥammad b. ʿAbdullāh al-Mukharrimī > Yaḥyá b. Ādam > Ḥafṣ > Ashʿath > ʿAṭāʾ

[Machine] The translation of the given passage "أَكْثَرُ الْحَيْضِ خَمْسَةَ عَشَرَ" into English is: "Most of the menstruation is fifteen."  

البيهقي:١٥٤٠٧ – أَخْبَرَنَا أَبُو بَكْرِ بْنُ الْحَارِثِ أنا عَلِيُّ بْنُ عُمَرَ الْحَافِظُ نا إِبْرَاهِيمُ بْنُ حَمَّادٍ نا مُحَمَّدُ بْنُ عَبْدِ اللهِ الْمُخَرِّمِيُّ نا يَحْيَى بْنُ آدَمَ نا حَفْصٌ عَنْ أَشْعَثَ عَنْ عَطَاءٍ قَالَ

أَكْثَرُ الْحَيْضِ خَمْسَةَ عَشَرَ