In tracing the story down it seems that the main witness was Assouline. As described by the American Council for Judaism in a book review of Robert Satloff's Among the Righteous:
In Paris, a grand mosque built in honour of the 100,000 Muslim soldiers who died fighting for France in the First World War, became a sanctuary for Jews escaping persecution less than three decades later. Si Kaddour Benghabrit was a French Algerian who was deeply loyal to France. During World War I, he was appointed honourary consul-general and served the religious needs of Muslims in the French army. After the war came to an end, he worked in the French Ministry of Foreign Affairs until 1920, when the parliament decided to acknowledge his loyalty by asking him to establish a mosque in Paris. Six years later, the Great Mosque of Paris became a reality and Benghabrit was appointed its rector.
Si Kaddour Benghabrit
When war broke out in Europe again, and Jewish lives were in danger, Benghabrit used the mosque as a hiding place, issuing each person with a fake certificate of Muslim identity. One North African Jew named Albert Assouline who had escaped from a German prison camp, wrote of his experience hiding in the mosque, “No fewer than 1,732 resistance fighters found refuge in its underground caverns. These included Muslim escapees but also Christians and Jews. The latter were by far the most numerous.” Accounts differ on the number of those saved, yet it remains a shining story of human solidarity.
According to Assouline, he and an Algerian named Yassa Rabah escaped together from the camp and stealthily traversed the countryside across the French-German border, heading for Paris. Once in Paris they made their way to the mosque, where, evidently thanks to Rabah’s connections to the Algerian community, the two found refuge. Eventually Assouline continued his journey and joined up with Free French forces to continue the fight against the German occupation ... the most fantastic part of the story was his claim that the mosque provided sanctuary and sustenance to Jews hiding from the Vichy and German troops as well as to other fighters in the anti-Fascist resistance.This is a story of heroes that needs to be publicized.
In a 1983 article for Almanach due Combattant, a French veterans’ magazine, Assouline wrote [that] the senior imam of the mosque, Si Mohammed Benzouaou took “considerable risk” by hiding Jews and providing many (including many children) with certificates of Muslim identity, with which they could avoid deportation and certain death. Assouline recalled one “hot alert” when German soldiers smelled the odor of cigarettes and, convinced that Muslims were forbidden to smoke, searched the mosque looking for hidden Jews. According to Assouline, the Jews were able to escape via sewer tunnels that connected the mosque to nearby buildings.
In Satloff’s view, “Assouline’s stunning story described the mosque as a virtual Grand Central Station for the Underground Railroad of Jews in France...."
Derri Berkani, a French documentary film-maker, of Algerian berber origin, was so moved by the untold story of the mosque that he made the 1991 film “Une Resistance Oubliee: La Mosque de Paris” (The Forgotten Resistance: The Mosque of Paris). ...
Berkani adds many previously unknown details: that Benghabrit had a special button installed that he would push to trigger a warning alarm in the event of a police raid and that, in emergencies, Jews would huddle in the mosque’s main sanctuary, which was known to be off-limits to non-Muslims, including German soldiers. In addition, Berkani provides the testimony of a physician in the municipal department of public hygiene, a man named Ahmed Somia, who tells the story of a young Jewish orphan, 7 or 8 years old, whom Benghabrit hid in the safety of his home. “Si Kaddour felt that we had to do something for this child,” he said. The solution was to provide the boy with a false birth certificate from the mosque that certified him as a Muslim and allowed him to live openly.
Another case is that of Salim (Simon) Halali, a world-renowned singer, who died in Cannes, France in 2005. Born in 1920 to a poor Jewish family in Annaba, near the Algerian-Tunisian border, he made his way to France when he was just 14. It was not long before Halali became France’s most celebrated “oriental” singer. For the next 40 years, he was a fixture of Andalusian music. It seems that he owed his success, and his life, to the mosque of Paris.
Virtually every obituary of Halali, on both sides of the Mediterranean, told the same story: Halali escaped certain deportation and death thanks to the generosity and ingenuity of Benghabrit. French writer Nidam Abdi explained in the Paris newspaper Liberation that the 20-year-old Halali found himself all alone in 1940 after his closest friend joined Radio Berlin, the Nazis’ premier propaganda organ. When Vichy started its pursuit of Jews, Halali turned to the mosque for help. Benghabrit, who had been a fan of Halali’s, evidently provided him with a certificate of Muslim identity. But because Halali was such a public figure, Benghabrit had to go one step further. To lend credibility to Halali’s claim of Muslim roots, Benghabrit arranged to have the name of Halali’s grandfather engraved on an abandoned tomb in the Muslim cemetery on Bobigny.
“For a certain number of Jews living in France — it is impossible to know how many — passing as Muslim was a clever ploy to avoid confiscation, arrest or deportation,” writes Satloff. “This was a particularly useful ploy for Jewish men, since Muslims, like Jews, are circumcised, often the defining test of Jewishness under Vichy rule.”
Satloff met in Paris with Dalil Boubakeur, the current rector of the Paris mosque and president of the governing body of all French Muslims, the Conseil Francais du Culte Musulman (CFCM).
When asked about the mosque’s role during World War II, he said that the reports of Jews being saved were true: “The mosque represented the sensibilities of the Muslims of North Africa toward their Jewish brothers. It was a natural phenomenon. ... What happened then (in the 1940s) was very symbolic but exemplary.”
Boubakeur noted that, “It is true that the mosque provided certificates of Muslim identity to some Jews. This was possible because, especially for North African Jews, the names are very close.” The motive, he said, was selfless, to enable Jews to avoid persecution by providing an acceptable rationale for their circumcision. The opportunity took advantage of a “double game” that, he said, characterized the complex relationship between the German occupation authorities and the Muslim community of Paris.
“The Germans were always pressing the mosque, trying to impose themselves on the mosque to use it for propaganda among Muslims,” he said. “They always wanted to have visitors here; at one point, we feared that Hitler himself would make a visit. We tried to resist but it wasn’t always possible.” Asked by Satloff if it was not courageous for the mosque to risk its status by helping Jews, Boubakeur replied: “Yes, yes, yes. Absolutely, it was courageous. It was very courageous. Courageous and natural at the same time.”
Boubakeur showed Satloff a copy of a document from the French Archives. Dated Sept. 24, 1940, the document was a note to the French minister of foreign affairs from the deputy director of the ministry’s Political Department. In it the writer — a bureaucrat identified by the initials “P.H.” — informed his superior about a certain peculiar action taken by the German authorities in Paris. The brief, typewritten note read as follows: “The occupation authorities suspect the personnel of the Mosque of Paris of fraudulently delivering to individuals of the Jewish race certificates attesting that the interested persons are of the Muslim confession. The imam was summoned, in a threatening manner, to put an end to all such practices. It seems, in effect, that a number of Jews resorted to all sorts of maneuvers of this kind to conceal their identity.”
Far from downplaying the role played by the mosque of Paris in rescuing Jews, Satloff points out that its Web site not only includes praise for the “active role” the mosque played during the war “in saving Jews and resistance fighters,” but there is also reference to “the late friend of the mosque, Abraham Assouline, (who) advanced the figure of 1,700 persons.”
A children's book was written about this episode, and a short film dramatizing it can be seen here.
(h/t Abdullah305 via Twitter)
UPDATE: Bataween at Point of No Return has more details.