"The leaders of the Islamic State and its soldiers have realised that the path to... victory is to be patient and resist the infidels whatever their alliances," said the person heard in the recording.
It was not clear when the message, released by the IS- affiliated Al-Furqan media group, was recorded.
In it, the apparent IS leader lashed out at "infidel nations headed by America, Russia and Iran" who, along with their allies, have inflicted losses on the jihadists during separate anti-IS offensives against IS in Syria and Iraq.
That recording, also released by Al-Furqan, was a rare sign of life from Baghdadi.
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In July, Moscow said it was struggling to confirm if Baghdadi was dead or alive, a month after reporting his possible demise in an air strike near the IS stronghold of Raqa in Syria.
Rumours have abounded about Baghdadi's own health and movements, but his whereabouts remain unclear.
The jihadists have since lost vast territory in both countries, including in Syria to Russia-backed regime troops and a US-supported Kurdish-Arab alliance.
But his group has claimed its members were behind deadly attacks carried out worldwide, including in Paris, London and Barcelona.