As explicated by Snopes.
Imran Chunawala was a devout Shi’ite Muslim. He prayed five times a day, kept all the holidays, and closed his perfume shop on holy days. One such holy day was the 21[sup]st[/sup] of Ramadan, commemorating the death of Iman Ali.
Mr. Chunwala put up a notice explaining why he wouldn’t be there that day. It was the same sign he put up every year, saying that on such-and-such English date the store would be closed for religious reasons.
As Dopers would put it, penis ensued. Mr. Chunwala was confused by the outrage, until he went back and reread his sign.
Hmmm, he said to himself, maybe I should have explained a bit more.