Some say it was impossible:
http://hoaxes.org/weblog/comments/did_ismail_the_bloodthirsty_really_father_888_childrenAccording to the Guinness Book of World Records, the 18th century Moroccan ruler Ismail the Bloodthirsty holds the record for being the most prolific father ever. He supposedly fathered 888 children, which means he had to father about 15 children a year for 60 years.
But Dorothy Einon, a researcher at University College London, argues in her article "How many children can one man have?" that even if Ismail had access to a steady supply of fertile women, it would have been impossible for him to father this many children.
But others say, yeah, he could have achieved it:
http://www.livescience.com/43661-how-sultan-sired-1000-kids.html
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0085292
http://www.ancient-origins.net/news-general/how-sultan-moulay-ismail-morocco-sired-1000-children-001386