Both Uses

Islam
in
The Other Wes Moore
(Edited)

The lower half of his face was shrouded by the long beard that he'd grown, an outward sign of the Islamic faith he'd adopted in prison.
p. 3.5 *

Islamic = related to the Muslim religion which is second most practiced in the world
He also pointed out that Wes had converted to Islam in jail and was a father of four children, whom he talked to almost every day on the telephone from jail.
p. 156.1

Islam = the Muslim religion; second most practiced religion in the world

Definitions:

(1) (Islam)
the monotheistic religious system of Muslims founded in Arabia in the 7th century and based on the teachings of Muhammad as laid down in the Koran; the world's second most practiced religion
(2) (meaning too rare to warrant focus)