"Scratch it, then rub it with water, then sprinkle water over it, and pray in it."  

عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ وَكَانَتْ تَكُونُ فِي حِجْرِهَا أَنَّ امْرَأَةً اسْتَفْتَتِ النَّبِيَّ ﷺ عَنْ دَمِ الْحَيْضِ يُصِيبُ الثَّوْبَ فَقَالَ حُتِّيهِ وَاقْرُصِيهِ وَانْضَحِيهِ وَصَلِّي فِيهِ  

"I heard Umm Qais bint Mihsan say that she asked the Messenger of Allah ﷺ about menstrual blood that gets on one's clothes. He said: 'Scratch it with a stick and wash it with water and lotus leaves.'"  

أَنَّهَا سَأَلَتْ رَسُولَ اللَّهِ ﷺ عَنْ دَمِ الْحِيضَةِ يُصِيبُ الثَّوْبَ قَالَ حُكِّيهِ بِضِلَعٍ وَاغْسِلِيهِ بِمَاءٍ وَسِدْرٍ