It is narrated from Amr bin Dinar (may Allah have mercy on him) that, according to the Companions of Muhammad (peace and blessings be upon him), al-quru' means menstruation. As for the view of Abdullah bin Umar (may Allah be pleased with them both), that al-quru' means the periods of purity, he took it from Zayd bin Thabit (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15399