A controversial South African mosque has performed its first interfaith marriage between a Muslim woman and a Christian man, in a ceremony denounced by local Islamic leaders. The imam of the Cape Town mosque, which bills itself as pluralistic and gender-equal, is challenging the idea that Islam bans such marriages, in defiance of traditional teachings on the issue.

Imam Taj Hargey, who founded Cape Town’s “Open Mosque” last year, is calling for Muslim clergy to prove that marriages between Muslim women and non-Muslim men are not permissible given the Quranic acceptance of marriages between Muslim men and women of other religions. “The reason why the Open Mosque allowed the historic occasion to occur is because in Islam, we either have gender equality or we don’t,” he told South Africa’s Eyewitness News on Monday.

The mosque officiated the marriage of Saieda Osman and Siegfried Milbert on Saturday after a number of other mosques refused them an Islamic wedding ceremony. Milbert, a Christian, chose not to convert to Islam to marry Osman.

"Everybody knows that such a marriage is not permissible in Islam," Riad Fataar, a senior leader of South Africa’s Muslim Judicial Council, told the Anadolu news agency. "It is ridiculous to think otherwise." Other members of the country’s Muslim community echoed the view, particularly taking issue with Milbert’s decision not to convert.

Most Islamic scholars agree that Muslim men are allowed to marry "women of the book," in reference to Christian and Jewish women. But Muslim women are generally believed to be forbidden from marriages to non-Muslims unless the man converts to Islam first. Some men nominally convert to circumvent the prohibition.

Hargey disputes this, however, arguing that "there is no verse in the Holy Quran that bans Muslim women from marrying non-Muslim men." The imam previously conducted marriage ceremonies in the U.K. for Muslim women marrying Christian or Jewish men without requiring the non-Muslim partners to first convert. Many Muslims view these unions as tantamount to living in sin.

The imam’s mosque, located in Cape Town’s Wynberg suburb, has also challenged other widespread conventions in Islamic practice with the aim of promoting a culture of tolerance to combat radicalism. The Open Mosque allows men and women to pray together in the same hall without partitions and encourages the participation of LGBT Muslims in the mosque’s religious life (while still drawing the line at performing same-sex marriages).

The effort has prompted criticism from Muslims in the country, along with some death threats. Hargey’s detractors have referred to him as a “heretic” and criticized him for promoting a “pro-gay agenda.” South Africa’s Muslim community numbers about 737,000, making up around 1.5 percent of the country’s population.