Recently, while touring the U.S. and Canada, London's first Muslim mayor, Sadiq Khan, "attacked anti-Muslim views and policies and argued that what is needed is to build 'bridges rather than walls' – a reference to Mr. Donald Trump's proposal to build a wall along the US-Mexico border."

He specifically and repeatedly criticized the notion "that it is not possible to hold Western values and to be a Muslim."  This notion, which he attributed to Trump, plays "into the hands of Daesh and so-called ISIS because it implies it's not possible to be a Western liberal and mainstream Muslim."

Can Muslims hold to Western liberal values and still be true to mainstream Islam? 

This pivotal question is easily answered by determining what is and is not Islamic.  Muslims have traditionally accomplished this by asking the following questions: what do the core texts of Islam say about the thing in question – call it "X"?  Does the Koran, believed by Muslims to contain the literal commands of Allah, call for or justify X?  Do the hadith and sira texts – which purport to record the sayings and deeds of Allah's prophet, whom the Koran (e.g., 33:21) exhorts Muslims to emulate in all ways – call for or justify X?

If any ambiguity still remains concerning X, the next question becomes: what is the consensus (ijma') of the Islamic world's leading authorities concerning X?  Here one must often turn to the tafsirs, or exegeses of Islam's most learned men – the ulema – and consider their conclusions.  Muhammad himself reportedly said, "My umma [Islamic nation] will never be in agreement over an error."

For example, the Koran commands believers to uphold prayers; accordingly, all Muslims are agreed that Muslims need to pray.  Yet the Koran does not specify how many times.  In the hadith and sira, however, Muhammad makes clear that believers should pray five times.  And the ulema, having considered all these texts, are agreed that Muslims are to pray five times a day.

Thus, it is most certainly Islamic for Muslims to pray five times a day.  While both Muslim and Western scholars of Islam readily accept the aforementioned methodology (in Arabic known as usul al-fiqh) as foundational to determining what is Islamic – prayer is in the Koran, Muhammad clarified its implementation in the hadith, and the ulema are agreed to it – whenever the thing in question goes against Western values, then this standard approach to ascertaining what is and is not Islamic is wholly ignored.

In reality, however, countless forms of behavior that directly contradict Western values are called for in the Koran and/or hadith, and the ulema are agreed to it: death to apostates and blasphemers, subjugation of Muslim women, sexual enslavement of non-Muslim women, polygamy, child marriage, ban on and destruction of non-Muslim places of worship and scriptures, and enmity for non-Muslims – are all no less Islamic than prayer is. 

Even Islamic State atrocities – such as triumphing over the mutilated corpses of "infidels" and smiling while posing with their decapitated heads – find support in the Koran and stories of the prophet.

To fully appreciate how much of Islam directly contradicts Western values, consider the findings of one Arabic language article by Dr. Ahmed Ibrahim Khadr.  It lists a number of things that mainstream Muslims support even though they directly contradict Western values.  These include: demands for a caliphate that rules according to sharia and expands into "infidel" territory through jihad, death for anyone vocally critical of Islam or Muhammad, death for Muslims who try to leave Islam, rejection of any equality for Christians and Jews in a Muslim state, rejection of any equality for women with men, and so forth.

Anyone who understands how Islam is actually articulated – such as London's Muslim mayor, Sadiq Khan – knows that the assertion that it is "possible to be a Western liberal and mainstream Muslim" is a grotesque oxymoron.  It's akin to saying it's possible to fit a square peg through a round hole.  It's not – unless, of course, one forcefully hammers it through, breaking portions of the peg (the Muslim) and cracking the surface of the hole (Western society). 

It is disingenuous to accept the well-known methodology of Islamic jurisprudence – is X part of the Koran, hadith, and/or sira, and does it have consensus among the ulema? – but then to reject this same methodology whenever X is something that clearly contradicts Western values, as much of Islam is wont to do.

Raymond Ibrahim, author of The Al Qaeda Reader and Crucified Again, is a Shillman fellow at the David Horowitz Freedom Center and a Rosen fellow at the Middle East Forum.