Praise be to Allah.
Shaykh Muhammad ibn ‘Uthaymeen (may Allah have mercy on him) said:
This action is not permissible. The woman who intends to do ‘Umrah is not permitted to pass the meeqaat without entering ihraam; even if she is menstruating, she should enter ihraam whilst she is menstruating, and her ihraam is valid. The evidence for that is the fact that Asma’ bint ‘Umays, the wife of Abu Bakr (may Allah be pleased with them both) had given birth, and the Prophet (peace and blessings of Allah be upon him) had stopped in Dhu’l-Hulayfah on his way to the Farewell Pilgrimage. She sent word to the Prophet (peace and blessings of Allah be upon him) asking what she should do. He said, “Do ghusl and bandage your private part with a cloth and enter ihraam.”
The blood of menstruation is like the bleeding following childbirth, so we say to the woman who is menstruating: If you pass by the meeqaat and you are intending to do ‘Umrah or Hajj, then do ghusl and bandage your private part with a cloth and enter ihraam.
“Bandage your private part with a cloth” means tying a piece of cloth over the vagina, then entering ihraam, whether for Hajj or ‘Umrah.
But if you enter ihraam and reach Makkah, you should not go to the Ka’bah or do tawaaf, until you have become pure (i.e. until your period ends). Hence the Prophet (peace and blessings of Allah be upon him) said to ‘Aa’ishah when she was menstruating during ‘Umrah, “Do everything that the pilgrims do but do not circumambulate the House until you become pure.” This was narrated by al-Bukhaari and Muslim. In Saheeh al-Bukhaari it also says that ‘Aa’ishah said that when she became pure she circumambulated the House and did saa’i between al-Safa and al-Marwah. This indicates that when a woman enters ihraam for Hajj or ‘Umrah when she is menstruating, or if her period comes before she does tawaaf, then she should not do tawaaf or saa’i until she becomes pure (i.e., her period ends) and she does ghusl. But if she does tawaaf when she is taahir (pure) and her period comes after she has finished tawaaf, she should go on and do saa’i even if she is menstruating, then she should cut her hair and end her ‘Umrah, because tahaarah (purity) is not a necessary condition of saa’i between al-Safa and al-marwah.
From Sitteen Mas’alah ‘ala’l-Hayd.