Sunan Abi Dawud 20787
In-book no 283حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ الْقَعْنَبِيُّ، عَنْ مَالِكٍ، عَنْ هِشَامٍ، بِإِسْنَادِ زُهَيْرٍ وَمَعْنَاهُ وَقَالَ " فَإِذَا أَقْبَلَتِ الْحَيْضَةُ فَاتْرُكِي الصَّلاَةَ فَإِذَا ذَهَبَ قَدْرُهَا فَاغْسِلِي الدَّمَ عَنْكِ وَصَلِّي " .
This tradition has also been transmitted by Zuhair through a different chain of narrators, to the same effect. He said: When the menstruation begins, you should abandon prayer; when the period equal to its length of time passes, you should wash away the blood and pray.