The man stood at the podium in the cramped Masjid Un-Noor mosque on Staten Island as hundreds of Muslims sat barefoot on the carpet before him, facing east, just before the start of Friday prayers. In his outstretched right hand, he held up a tiny American flag and a pocket-size copy of the Constitution.

“This unites us,” said the man, Suhail Muzaffar, a leader at the mosque. “It is not Christian, it is not Buddhist, it is not Muslim.”

“Please,” he added. “Find time to look at this document.”

The scene, charged with symbolism, had a familiarity for many in the crowd. After the services, one man in the congregation approached Mr. Muzaffar and told him, “You looked just like Khizr Khan.”

He was referring, of course, to the Pakistani immigrant whose tribute to his son, an Army captain killed in combat, electrified the Democratic National Convention in what became a memorable moment in the presidential campaign, caused sales of pocket-size copies of the Constitution to skyrocket and galvanized American Muslims eager to answer the anti-Muslim rhetoric of Donald J. Trump, the Republican presidential nominee.