The Islam did arrive in Somalia before Medina Al munawara in Saudi Arabia. I can't exactly say when was that, however it is clear that it was centuries ago, maybe 1500 years ago . Partially because Somalia is the only country in the world which has the people who are 100% Muslims, except Saudi Arabia, due to the time that the Islam arrived in Somalia and the Somali people who believe in that the Islam is a way of life. More than that, almost every Somali person knows the Qurán by heart than any other muslim country on earth. They are actually very proud to be a Muslims.