The official Facebook page and Twitter account of former Islamist President Mohamed Morsi published a message Thursday evening calling on his supporters to continue "the revolution."
The message was allegedly sent from prison where he is facing a death sentence.
"My strength and my determination have not weakened yet and my belief in victory is limitless," Morsi is reported to have said.
The ousted president was sentenced to death in July after being convicted on counts of murder and attempted murder in the 2011 prison escape case.
In the same month, he was given a life sentence in a case related to charges of spying for Hamas.
Morsi was also sentenced in April to 20 years in prison for inciting the violence that led to the death of ten people during clashes outside the Ittihadiya presidential palace in December 2012.
"Your revolution is going to be studied by all the people of the world, so complete it, as it will free the nation," he added.
The leading Muslim Brotherhood figure concluded his message by referring to himself as the President of the Arab Republic of Egypt and congratulated the people on Eid Al-Fitr, the end of the holy month of Ramadan.
Ousted in July 2013 by the opposition and army amidst popular protests, the Muslim Brotherhood figure is facing a number of trials.
This is the third alleged message from Morsi since his imprisonment in 2014.