The following lessons cover the book Usool as-Sunnah (Foundations of the Sunnah) of Imaam Ahmad, rahimahullah, as explained by our noble Shaykh Rabee bin Haadee al-Madkhalee, hafidhahullah.
You can download the Arabic text here: شرح أصول السنة للإمام أحمد بن حنبل