Sunan an-Nasa'i, hadith 208

أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، عَنْ أُمِّ سَلَمَةَ، تَعْنِي أَنَّ امْرَأَةً، كَانَتْ تُهَرَاقُ الدَّمَ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَاسْتَفْتَتْ لَهَا أُمُّ سَلَمَةَ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏ "‏ لِتَنْظُرْ عَدَدَ اللَّيَالِي وَالأَيَّامِ الَّتِي كَانَتْ تَحِيضُ مِنَ الشَّهْرِ قَبْلَ أَنْ يُصِيبَهَا الَّذِي أَصَابَهَا فَلْتَتْرُكِ الصَّلاَةَ قَدْرَ ذَلِكَ مِنَ الشَّهْرِ فَإِذَا خَلَّفَتْ ذَلِكَ فَلْتَغْتَسِلْ ثُمَّ لْتَسْتَثْفِرْ ثُمَّ لْتُصَلِّي ‏"‏ ‏.‏

It was narrated from Umm Salamah that a woman suffered constant bleeding at the time of the Messenger of Allah (ﷺ), so Umm Salamah consulted the Prophet (ﷺ) for her. He said:"Let her count the number of nights and says that she used to menstruate each month before this happened to her, and let her stop praying for that amount of time each month. Then when that is over let her perform Ghusl, then let her use a pad, and pray