In traditional Islamic dream interpretation, a Muslim woman's vagina is understood to be the doorway, through which Allah has commanded all Muslims to pass, as verse 2:189 of the Qur’an says: "So come to the houses by their doors".
The vulva (farj) means "relief (faraj) for whoever is in distress." And the vulva is the mihrab (prayer niche in a mosque) and the qiblah (the direction of Mecca toward which one faces in prayer).
In the wall of a mosque facing toward's Mecca, the mihrab is like a vagina recessed into the wall to show the direction of prayers for Muslims. Thus in traditional Islam, the yoni is associated with the most sacred rite of Islam, the daily prayers.
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Reference: See the Islamic dream interpretation book, "Ta‘tîr al-anâm fî ta‘bîr al-manâm", by 17th-century Sufi scholar 'Abd al-Ghani al-Nabulusi, 5th ed. (Beirut: Dar al-Khayr, 1991), p. 358-359, for this symbolism.
