Asma' daughter of Abu Bakr said: A woman asked the Messenger of Allah (ﷺ): Messenger of Allah, what do you think if the clothe of any of us smeared with the blood of menstruation; what should she do ? He said: If (the clothe of) any of you is smeared with blood of menstruation, she should scratch it; then she should sprinkle water upon it and then she may pray.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ فَاطِمَةَ بِنْتِ الْمُنْذِرِ، عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ، أَنَّهَا قَالَتْ سَأَلَتِ امْرَأَةٌ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَتْ يَا رَسُولَ اللَّهِ أَرَأَيْتَ إِحْدَانَا إِذَا أَصَابَ ثَوْبَهَا الدَّمُ مِنَ الْحَيْضَةِ كَيْفَ تَصْنَعُ قَالَ " إِذَا أَصَابَ إِحْدَاكُنَّ الدَّمُ مِنَ الْحَيْضِ فَلْتَقْرِصْهُ ثُمَّ لْتَنْضَحْهُ بِالْمَاءِ ثُمَّ لْتُصَلِّي " .
sunnah.com