The Syrian Observatory for Human Rights said the cleric, known by the nom-de-guerre Abu Musab al-Jazrawi, raised objections during a meeting yesterday to the way pilot Maaz al-Kassasbeh was killed.
"He raised objections during the weekly meeting that takes place between clerics and IS leaders in the Aleppo area," said Observatory director Rami Abdel Rahman.
"He said the way Kassasbeh had been killed violated religious traditions."
Kassasbeh was captured by IS in December after his plane went down over Syria as he participated in the US-led coalition fighting the jihadist group.
Abdel Rahman said Jazrawi was removed from his post after the criticism, and could also face a religious tribunal and possible punishment.
IS and its supporters have sought to produce religious justifications for the horrific method by which they killed Kassasbeh, but ordinary Muslims and Islamic scholars have fiercely criticised the execution.
The group emerged in Syria in 2013, and rules a self-proclaimed Islamic "caliphate" in territory under its control in Iraq and Syria.
