Al-Azhar's grand sheikh said he rejects any boycott of the first post-25 January uprising presidential election after casting his ballot Wednesday.
Ahmed al-Tayyeb said it is forbidden not to cast a ballot if you are an eligible voter with the ability to do so.
Tayyeb described election participation as a responsibility, noting that bribing or attempting to influence voters is illegal.
The first day of voting was a historic day, Tayyeb said, as it was the first time Egyptians were able to choose their president in a fair, democratic election. He also called on citizens to be committed to whatever outcome the election yields.
Voter turnout appeared low on the first day of voting, but increased later in the day on Wednesday.
The Cabinet announced Wednesday that state employees would be given a day off on Thursday so they can vote.