A vocal anti-Israel activist, who has made several donations to Rep. Rashida Tlaib's, D-Mich., House campaigns, mourned the assassination of a top Hamas leader on Wednesday, saying his "martyrdom is not in vain."

Zahra Billoo, a disgraced former Women's March leader and the executive director of Council on American-Islamic Relations (CAIR) in San Francisco, took to social media after it was reported that Hamas leader Ismail Haniyeh was assassinated in Tehran, Iran, prompting Iranian Supreme Leader Ali Khamenei to vow "revenge" for the attack.

 "Never say that those martyred in the cause of Allah are dead—in fact, they are alive! But you do not perceive it," Billoo said in the first part of her post, appearing to quote the Quran. 

"Tonight, we mourn Ismail himself but know his martyrdom is not in vain," she continued, using a controversial phrase pushed by anti-Israel activists to mean the elimination of Israel. "From the river to the sea, Palestine will be free."

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"I mourn yesterday’s martyrs because I can see the horrific path killing peace negotiators leads to," Billoo added in a follow-up X thread, accusing Israel of a "genocide."

Billoo's initial post immediately drew backlash from social media users, with some people mocking the Quran quote and saying the Hamas leader is definitely "not alive." 

"Probably important to remember this, too, whenever you see the name CAIR," journalist Bari Weiss said.

Billoo, who has donated almost $1,000 to multiple Tlaib campaigns, has been a lightning rod of controversy in recent years over her anti-Israel rhetoric, which led to the left-wing Women's March board severing ties with her in 2019 after only serving two days. She posted a 25-post Twitter thread at the time blaming her ouster on an "Islamophobic smear campaign" and "right-wingers."

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Despite the backlash, Tlaib came to Billoo's defense the day after the ouster, posting, "#FreePalestine always sis! They won't silence us for speaking out against human rights violations."

"They will lie, smear our names and call us anti this and that, but we always be pro-humanity & we have the truth on our side. Stay strong," she continued.

Several of Billoo's controversial posts were circulating on social media shortly after she was announced as a Women's March board member.

"If you support Israel, you are no doubt supporting baby killers," Billoo wrote in one unearthed 2014 post that was circulating ahead of the ouster. In other posts she described Zionism as "racism" and said she was a "proud anti-Zionist."

"In looking at the tweets in question, I acknowledge that I wrote passionately. While I may have phrased some of my content differently today, I stand by my words," Billoo said in 2019 about several of her controversial posts.

Prior to the Women's March controversy, Billoo took a "selfie" with Tlaib outside her Washington, D.C., congressional office in early 2019 and said, "Not all sheros wear capes, some like Rep. [Tlaib] wear Congressional pins!"

"So good to see you sis! I will always speak truth to power because I got you to protect," Tlaib responded.

Billoo was also in attendance at a Tlaib fundraising event in California in 2021, according to a Facebook post.

This is not the first time a CAIR leader has ignited backlash on social media. Last December, Nihad Awad, the executive director and co-founder of CAIR, said he was "happy to see" the Oct. 7 Hamas invasion of Israel and that the Jewish state did not have a right to self-defense because it is an "occupying power."

"And yes, the people of Gaza have the right to self-defense — have the right to defend themselves. And yes, Israel as an occupying power does not have that right to self-defense," he said.

In addition to Billoo's anti-Israel rhetoric, she has also repeatedly attacked Memorial Day and smeared the U.S. military, questioning why fallen soldiers should be remembered.

"You think we should honor people who commit war crimes?" she asked in one post.

"Did not and does not celebrate #MemorialDay," Billoo posted in a long 2019 thread. "There cannot be any honor earned through participation in dishonorable wars."

Tlaib's office did not respond to Fox News Digital's request for comment.

Fox News' Aubrie Spady and Landon Mion contributed to this report.