Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
If you intend to perform Hajj al-Tamattu` but begin menstruating before completing the `Umrah, your Hajj automatically becomes Hajj al-Qiran—no formal intention change is required. This ruling is based on the Prophet Muhammad’s (peace be upon him) guidance to `Aishah (may Allah be pleased with her).
Responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
When menstruation delays your `Umrah Tawaf, you remain in Ihram and combine both the `Umrah and Hajj rites into one continuous state.
After your menstruation ends, you perform one Tawaf and Sa`i that counts for both `Umrah and Hajj, and you offer the required sacrificial animal (hadi). Switching to Hajj al-Ifrad is not permitted in this case. However, if your purity returns before the 9th of Dhul-Hijjah with sufficient time to complete your `Umrah Tawaf separately, you may revert to performing Hajj al-Tamattu` as originally intended.
In summary, menstruation during Hajj al-Tamattu` automatically converts it to Hajj al-Qiran, allowing you to complete both `Umrah and Hajj within a single Ihram.
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Almighty Allah knows best.