Haroon Moghul is a fellow at the Institute for Social Policy and Understanding . He is an author, essayist and public speaker. Follow him @hsmoghul . The opinions expressed in this commentary are solely those of the author.

(CNN) Muslims will be fasting this Friday. It's Ashura, the 10th day of the first month on the Islamic calendar. Islamic tradition holds that the Prophet Mohammed encountered Jews fasting on this day, who told them they were marking the Hebrews escape from Egypt, and he decided to join them.

While the Islamic tradition teaches the Exodus occurred on Yom Kippur (in Judaism, the day of atonement) Jews actually commemorate the Hebrews' escape from Egypt on Passover.

If you're wondering why Muslims would celebrate a Jewish holiday, that's because neither Mohammed nor the early Muslims saw themselves as part of a new faith community.

They were a reboot, the restoration of monotheism to its original factory settings. Mohammed described himself as concluding the line of prophecy that went way back to Adam in the Garden of Eden and includes Noah and Abraham. Moses and Jesus, too: They're named much more often in the Quran than Mohammed is.

Ashura also has another, grimmer meaning for Muslims: it marks the day the Prophet Mohammed's grandson was killed after a failed uprising against a corrupt caliph.

For Sunni Muslims, that event was a tragedy. For Shia Muslims, it's even worse: The family of the Prophet was denied its right to lead, but this time by blood and sword. So this Friday is, for all Muslims, a day of deliverance and a day of sorrow, of freedom -- and tyranny.

After the Prophet Mohammed's death in 632, his closest companions struggled to keep control of his community. Shia Muslims believe his cousin, Ali, was meant to be the first ruler; the majority went with the Prophet's father-in-law, Abu Bakr.

Despite the dispute, Islam was surging so quickly that soon the old believers were overwhelmed by a surge of new converts, all of whom came for different reasons. Piety, maybe. But also prestige and power.

Forty years after Mohammed passed on, a king ruled in the guise of a Caliph, arrogating himself to powers Muslims judged pharaoh-like. (There's no greater Quranic symbol of tyranny than Moses' nemesis.)

Rather than rule in a simple, egalitarian fashion, like his predecessors and the Prophet whose memory was still alive and well, the fifth caliph, Muawiya, built palaces and shut himself off from his people.

To add insult to injury, he appointed his own son, Yazid, to succeed him on his death.

Hussain, who saw his grandfather's legacy almost undone, journeyed to southern Iraq, where he'd meet up with his followers to challenge Yazid's claim.

Hussain was David. Yazid's army was Goliath. There would, however, be no slingshot. No parting of the waters. On the same day Mohammed asked Muslims to remember God's rescue of their forefathers from Pharaoh, the Caliph's army crushed the revolt of the Prophet's grandson and secured his dynasty for decades more.

In a world obsessed with narratives of "us" and "them," of civilizations clashing and great blocs feuding, sorting us into mutually exclusive categories -- Islam or the West, the global South versus the global North -- this darker side of Ashura isn't just important. It's critical.

I know a lot of Muslims who demand the West own up to its sins. They expect Western schools, institutions and leaders to acknowledge the dark side of our history. The expansionism, imperialism, colonialism.

I wonder, though, if we could tolerate the same introspections in our mosques and madrasas. It's easy to talk about being the victim. It's a lot harder to talk about doing wrong. It's easy to talk about what other people do to you. It's hard to talk about what we do to others. Or what's done in our name.

When I was young, I was taught about Islam as a catalog of battles and conquests, rules and rituals. There was little serious ethical deliberation, not much in the way of cultural direction and precious little spiritual content.

Partly that's because some Muslims have confused religion for ethnicity and treat our scripture as nationalist mythology. Some Islamic movements have twisted Islam into a political program and prefer it that way.

But partly because it's just easier to look at the upside. The first Caliph, Abu Bakr, died of natural causes. He lucked out: The second Caliph, Umar, was assassinated. The third, Uthman, was killed, too, except by his own troops. The fourth, Hussain's father, Ali, was assassinated by radical Muslims -- the Khawarij, the precursors of ISIS -- while in prayer. And then there was Hussain.

Who wants to focus on this history?

Forget the clash of civilizations. The greater battles are between what we say we stand for and what we do actually do, between the values we proclaim and the realities we impose.

Today, Syrians die by the thousands, attacked by a Ba'athist regime uncritically supported by the Islamic Republic of Iran. A revolution that came to power calling the despotic shah a tyrant has now inaugurated a regime with a more murderous record. Iran, with its allies in Syrian President Bashar al-Assad and Hezbollah, have killed and tortured more than even ISIS has. Like ISIS, too, it happens in my religion's name. It's Yazid versus Yazid, though both pretend to be Hussain, righteous warriors for justice.

The great fault lines of our times aren't between religions and nationalities but within them. But before you read this as an excuse to pile on the Muslim world, remember that the same lessons apply to all peoples and places. Including our own.

There's a Hussain in Edward Snowden, who brought our secrets to the light. There's a Hussain in Occupy Wall Street, asking us where our values of fairness and fair play have gone. There's a Hussain in #BlackLivesMatter, forcing us to face up to the racism we insist we've overcome. There's a Hussain in the Israeli youth who refuse to serve in an occupying regime. There's a Hussain in Palestinians who refuse to give up their rights.

And all these Hussains? They might lose. They might never see the outcome of their struggles. Not here, at least. Some pharaohs meet the sea, while others pass away in their palaces, peacefully.

Like many prophets and preachers, Mohammed taught that those whose prayers are not answered in this life will be heard in the next. Justice might be postponed, but it will never be denied.

(This post has been edited to clarify the relationship between Yom Kippur and Passover in Judaism.)