It is the second to Christianity.
It is claimed that Christianity is the religion with more followers and Islam is the second.
The worlds largest religion is Christianity and the second is Islam
The second book of Christianity is called Exodus.
Islam is the second major religion, although far behind the leading religion, Christianity (mainly Catholicism).
Islam is the second largest religion: behind Christianity
The second-largest religion, worldwide, is Islam.
Christianity is the second most common religion in Africa, with Islam being the most common.
I believe their top religion is Christianity and their second is Islamic.
Christianity and the second largest Islam.
Basically any other religion besides Christianity, Judaism and Islam since all three religions believe in the first part (the old testament) and once you get to the second part that's when the beliefs divide.
If you mean per the world number of followers, then Islam religion is the second to Christianity.