How does one make the intention for fasting the first nine days of Dhul-Hijjah and breaking the fast on the day of Eid with sacrifice? Is Ihram required? And does the reward for fasting these days diminish if one's menstrual period begins?

The intention (niyyah) is formed by resolving to perform an act, and its place is the heart; it is not recommended to utter it verbally. It is from the Sunnah for one who intends to offer a sacrifice (udhiyyah) not to take from their hair or nails until their sacrifice has been slaughtered. The reward for fasting is attained through a sincere intention, even if one is unable to fast due to menstruation, based on the Prophet's (peace be upon him) saying: "Whoever intended to perform a good deed but did not do it, Allah records it for him as a complete good deed."