Leaping down the stairs on Sept. 11, 2001, when he had been installing ceiling speakers for a reinsurance company on the 49th floor, Mr. Abdus-Salaam had a brief, panicked thought. He didn’t see any of the Muslims he recognized from the prayer room. Where were they? Had they managed to evacuate?  He staggered out to the gathering place at Broadway and Vesey. From that corner, he watched the south tower collapse, to be followed soon by the north one. Somewhere in the smoking, burning mountain of rubble lay whatever remained of the prayer room, and also of some of the Muslims who had used it.  Given the vitriolic opposition now to the proposal to build a Muslim community center two blocks from ground zero, one might say something else has been destroyed: the realization that Muslim people and the Muslim religion were part of the life of the World Trade Center.  Opponents of the Park51 project say the presence of a Muslim center dishonors the victims of the Islamic extremists who flew two jets into the towers. Yet not only were Muslims peacefully worshiping in the twin towers long before the attacks, but even after the 1993 bombing of one tower by a Muslim radical, Ramzi Yousef, their religious observance generated no opposition  “We weren’t aliens,” Mr. Abdus-Salaam, 60, said in a telephone interview from Florida, where he moved in retirement. “We had a foothold there. You’d walk into the elevator in the morning and say, ‘Salaam aleikum,’ to one construction worker and five more guys in suits would answer, ‘Aleikum salaam.’ ”  One of those men in suits could have been Zafar Sareshwala, a financial executive for the Parsoli Corporation, who went to the prayer room while on business trips from his London office. He was introduced to it, he recently recalled, by a Manhattan investment banker who happened to be Jewish.  “It was so freeing and so calm,” Mr. Sareshwala, 47, said in a phone conversation from Mumbai, where he is now based. “It had the feel of a real mosque. And the best part is that you are in the epicenter of capitalism — New York City, the World Trade Center — and you had this island of spiritualism. I don’t think you could have that combination anywhere in the world.”  How, when and by whom the prayer room was begun remains unclear. Interviews this week with historians and building executives of the trade center came up empty. Many of the Port Authority’s leasing records were destroyed in the towers’ collapse. The imams of several Manhattan mosques whose members sometimes went to the prayer room knew nothing of its origins.  Yet the room’s existence is etched in the memories of participants like Mr. Abdus-Salaam and Mr. Sareshwala. Prof. John L. Esposito of Georgetown University, an expert in Islamic studies, briefly mentions the prayer room in his recent book “The Future of Islam.”  Moreover, the prayer room was not the only example of Muslim religious practice in or near the trade center. About three dozen Muslim staff members of Windows on the World, the restaurant atop the north tower, used a stairwell between the 106th and 107th floors for their daily prayers.  Without enough time to walk to the closest mosque — Masjid Manhattan on Warren Street, about four blocks away — the waiters, chefs, banquet managers and others would lay a tablecloth atop the concrete landing in the stairwell and flatten cardboard boxes from food deliveries to serve as prayer mats.  During Ramadan, the Muslim employees brought their favorite foods from home, and at the end of the daylight fast shared their iftar meal in the restaurant’s employee cafeteria.  “Iftar was my best memory,” said Sekou Siby, 45, a chef originally from the Ivory Coast. “It was really special.”  Such memories have been overtaken, though, by others. Mr. Siby’s cousin and roommate, a chef named Abdoul-Karim Traoré, died at Windows on the World on Sept. 11, as did at least one other Muslim staff member, a banquet server named Shabir Ahmed from Bangladesh.  Fekkak Mamdouh, an immigrant from Morocco who was head waiter, attended a worship service just weeks after the attacks that honored the estimated 60 Muslims who died. Far from being viewed as objectionable, the service was conducted with formal support from city, state and federal authorities, who arranged for buses to transport imams and mourners to Warren Street.  There, within sight of the ruins, they chanted salat al-Ghaib, the funeral prayer when there is not an intact corpse.  “It is a shame, shame, shame,” Mr. Mamdouh, 49, said of the Park51 dispute. “Sometimes I wake up and think, this is not what I came to America for. I came here to build this country together. People are using this issue for their own agenda. It’s designed to keep the hate going.”  An earlier version of this article misspelled the name of the proposed Islamic center and mosque near ground zero. It is Park51, not Parc51. It also misstated the name of a chef at the Windows on the World restaurant who died on Sept. 11. He was Abdoul-Karim Traoré, not Abdul Karim. And the article misstated the order in which the World Trade Center towers fell. The south tower fell first, not the north tower.  A version of this article appears in print on September 11, 2010, on Page A12 of the New York edition with the headline: Muslims and Islam Were Part of Twin Towers’ Life. 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Muslim workers worshiped peacefully and without controversy for years in a room on the 17th floor of the south tower.