"If it is menstrual blood then it is blood that is black and recognizable, so stop prying, and if it is other than that then perform Wudu', for it is just a vein." (Using translation from Nasāʾī 362)  

لَهَا رَسُولُ اللهِ ﷺ «إِذَا كَانَ دَمُ الْحَيْضِ فَإِنَّهُ دَمٌ أَسْوَدُ يُعْرَفُ فَأَمْسِكِي عَنِ الصَّلَاةِ فَإِذَا كَانَ الْآخَرُ فَتَوَضَّئِي فَإِنَّمَا هُوَ عِرْقٌ» قَالَ مُحَمَّدُ بْنُ الْمُثَنَّى حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ هَذَا مِنْ كِتَابِهِ  

Urwah ibn az-Zubayr reported from Fatimah daughter of AbuHubaysh that her blood kept flowing, so the Prophet ﷺ said to her: When the blood of the menses comes, it is black blood which can be recognised; so when that comes, refrain from prayer; but when a different type of blood comes, perform ablution and pray, for it is (due only to) a vein. Abu Dawud said: Ibn al-Muthanna narrates this tradition from his book on the authority of Ibn 'Adi in a similar way. Later on he transmitted it to us from his memory: Muhammad b. 'Amr reported to us from al-Zuhri from 'Urwah on the authority of 'Aishah who said: Fatimah used to have her blood flowing. He then reported the tradition conveying the same meaning. Abu Dawud said: Anas b. Sirin reported from Ibn 'Abbas about the woman who has a prolonged flow of blood. He said: If she sees thick blood, she should not pray; if she finds herself purified even for a moment, she should was an pray. Makhul said: Menses are not hidden from women. Their blood is black and thick. When it (blackness and thickness) goes away and there appears yellowness and liquidness, that is the flow of blood (from vein). She should wash and pray. Abu Dawud said: This tradition has been transmitted by Sa'id b. al-Musayyab through a different chain of narrators, saying: The woman who has a prolonged flow of blood should abandon prayer when the menstruation begins; when it is finished, she should wash and pray. Sumayy and others have also reported it from Sa'id b. al-Musayyab. This version adds: She should refrain (from prayer) during her menstrual period. Hammad b. Salamah has reported it similarly from Yahya b. Sa'id on the authority of Sa'id b. al-Musayyab. Abu Dawud said: Yunus has reported from Al-Hasan: When the bleeding of a menstruating woman extends (beyond the normal period), she should refrain (from prayer), after her menses are over, for one or two days. Now she becomes the woman who has a prolonged flow of blood. Al-Taimi reported from Qatadah: If her menstrual period is prolonged by five days, she should pray. Al-Taimi said: I kept on reducing (the number of days) until I reached two days. He said: If the period extends by two days, they will be counted from the menstrual period. When Ibn Sirin was questioned about it, he said: Women have better knowledge of that. (Using translation from Abū Dāʾūd 286)   

رَسُولُ اللهِ ﷺ «إِنَّ دَمَ الْحَيْضِ دَمٌ أَسْوَدٌ يُعْرَفُ فَإِذَا كَانَ ذَلِكَ فَأَمْسِكِي عَنِ الصَّلَاةِ وَإِذَا كَانَ الْآخَرُ فَتَوَضَّئِي وَصَلِّي»  

"Fatimah bint Abi Hubaish suffered from Istihadah and she asked the Prophet ﷺ: 'O Messenger of Allah, I suffer from Istihadah and I do not become pure; should I stop praying?' The Messenger of Allah ﷺ said: 'That is a vein and is not menstruation. When your period comes, stop praying, and when it goes wash the traces of blood from yourself and perform Wudu'. That is a vein and is not menstruation.'" It was said to him: "What about Ghusl?' He ﷺ said: "no one doubts that." Abu 'Abdur-Rahman said: "I do not know anyone who mentioned 'and perform Wudu' in this Hadith except Hammad bin Zaid, for some others have reported it from Hisham, and they did not mention 'and perform Wudu' in it." (Using translation from Nasāʾī 217)  

اسْتُحِيضَتْ فَاطِمَةُ بِنْتُ أَبِي حُبَيْشٍ فَسَأَلَتِ النَّبِيَّ ﷺ فَقَالَتْ يَا رَسُولَ اللهِ إِنِّي أُسْتَحَاضُ فَلَا أَطْهُرُ أَفَأَدَعُ الصَّلَاةَ؟ فقَالَ رَسُولُ اللهِ ﷺ «إِنَّمَا ذَلِكَ عِرْقٌ وَلَيْسَتْ بِالْحَيْضَةِ فَإِذَا أَقْبَلَتِ الْحَيْضَةُ فَدَعِي الصَّلَاةَ فَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ أَثَرَ الدَّمِ وَتَوَضَّئِي فَإِنَّمَا ذَلِكَ عِرْقٌ وَلَيْسَتْ بِالْحَيْضَةِ» قِيلَ لَهُ فَالْغُسْلُ قَالَ وذَلِكَ يَشُكُّ فِيهِ أَحَدٌ قَالَ أَبُو عَبْدِ الرَّحْمَنِ لَا أَعْلَمُ أَحَدًا ذَكَرَ فِي هَذَا الْحَدِيثِ «وَتَوَضَّئِي» غَيْرَ حَمَّادِ بْنِ زَيْدٍ وَقَدْ رَوَى غَيْرُ وَاحِدٍ عَنْ هِشَامٍ وَلَمْ يَذْكُرْ فِيهِ وَتَوَضَّئِي  

[Machine] "O Messenger of Allah, I am not in a state of purification, so should I abandon prayer?" He said, "It is only menstruation." Khaled said in what I have read to him, "It is not considered as menstruation. So when the menstruation starts, leave the prayer, and when it ends, wash off the blood and then perform the prayer." Abu Abdur Rahman said, this hadith is narrated by Malik from Hisham from his father from Aisha, and it is the most authentic narration regarding menstruation. Also, Sulaiman narrated from Umm Salama, he did not hear it from Umm Salama, but there was a man between them.  

يَا رَسُولَ اللهِ إِنِّي لَا أَطْهُرُ أَفَأَتْرُكُ الصَّلَاةَ؟ قَالَ «إِنَّمَا هُوَ عِرْقٌ» قَالَ خَالِدٌ فِيمَا قَرَأْتُ عَلَيْهِ «وَلَيْسَتْ بِالْحَيْضَةِ فَإِذَا أَقْبَلَتِ الْحَيْضَةُ فَدَعِي الصَّلَاةَ وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ ثم صَلِّي» قَالَ أَبُو عَبْدِ الرَّحْمَنِ حَدِيثُ مَالِكٍ عَنْ هِشَامٍ عَنْ أَبِيهِ عَنْ عَائِشَةَ أَصَحُّ مَا يَأْتِي فِي الْمُسْتَحَاضَةِ وَحَدِيثُ سُلَيْمَانَ عَنْ أُمِّ سَلَمَةَ لَمْ يَسْمَعْهُ مِنْ أُمِّ سَلَمَةَ بَيْنَهُمَا رَجُلٌ