أَخْبَرَنَا حَجَّاجٌ، حَدَّثَنَا حَمَّادٌ، عَنْ يُونُسَ، عَنْ الْحَسَنِ، قَالَ: "إِذَا رَأَتْ الدَّمَ فَإِنَّهَا تُمْسِكُ عَنْ الصَّلَاةِ، تَعُدُّ أَيَّامِ حَيْضِهَا يَوْمًا أَوْ يَوْمَيْنِ، ثُمَّ هِيَ بَعْدَ ذَلِكَ مُسْتَحَاضَةٌ".
Imam Hasan al-Basri (may Allah have mercy on him) said: When she sees blood, she should stop praying, and after the days of menstruation, she should wait for one or two days; after that, she will be considered as experiencing istihada (irregular bleeding).