Hassan al-Banna: remember that Shias and Sunnis are all Muslims and the slogan of Tawhid (oneness) which are "There is no god but God" and "I bear witness that Muhammad is the Messenger of God" unites them. Shias and Sunnis are of the same stance regarding this basic ideological principle. The differences between these two factions are about the ancillaries and issues that can be resolved.
Zekriat la Mazkarat, p.250