Is it permissible to call a person in a state of major ritual impurity (junub) or a menstruating woman (ha'id) "najis" (impure), and is the fast of a person in a state of major ritual impurity accepted if they remain in that state from before dawn until after sunset?

It is not permissible to describe a Muslim in a state of major ritual impurity (junub) or a menstruating Muslim woman (ha'id) as impure (najis); because of the hadith (definition): "The believer does not become impure (najis)," and this hadith is a great principle regarding the purity of the Muslim, whether alive or dead. As for the ruling on fasting for someone in a state of major ritual impurity, it is valid, but it is not permissible for him to delay purifying himself from major ritual impurity so that he can perform the prayers.