Sunan Abu Dawud, hadith 283

حَدَّثَنَا 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