If confirmed, it would be Baghdadi's first message since reports said he was wounded earlier this year in Iraq.
Some analysts had said he was no longer running the group and others suggested he had died.
In the recording, issued by the group's al-Furqan media outlet and posted on several websites, a voice sounding like Baghdadi's says, "There is no excuse for any Muslim not to migrate to the Islamic State ... joining (its fight) is a duty on every Muslim."
"We are calling on you either join or carry weapons (to fight) wherever you are."
Al Jazeera could not independently verify the authenticity of the audio or its date.
In the message, Baghdadi tells the rulers of Saudi Arabia, who he considers his enemies, that "their end is near", adding that Persian Gulf rulers felt threatened by the growing popularity of his group.
ISIL has faced military setbacks in Iraq when Iraqi forces retook the city of Tikrit in the first big counter-offensive since ISIL rapidly seized swathes of territory last year.