Abdullah bin Umar (al-Umari) (may Allah have mercy on him) narrates from his brother, and from Yahya bin Sa'id (may Allah have mercy on him) and Rabi'ah (may Allah have mercy on him), that they said concerning the menstruating woman: At most she will refrain from prayer for fifteen days, then she will take the ritual bath and pray. Abdullah (may Allah have mercy on him) said: I found most people saying this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1541