سورة Al-Baqarah ( The Cow ) - الآية 222

And they ask you about menstruation. Say: It is a discomfort; therefore keep aloof from the women during the menstrual discharge and do not go near them until they have become clean; then when they have cleansed themselves, go in to them as Allah has commanded you; surely Allah loves those who turn much (to Him), and He loves those who purify themselves.