Sunni Islam upholds injunctions against the representation of divinity, or of biblical and Quranic prophets. This prohibition against "graven images" is essentially rooted in a belief that only God has Creative power, and that it is particularly blasphemous to portray or paint pictures of prophets or of God himself. However, a few observations about this issue are important to clarify at the outset of any discussion of symbolism in Sunni culture.
Other traditions have dealt with the possibility or impossibility of representing the divine, most notably in the iconoclastic controversy in medieval Byzantium. Also, while it is true that the vast majority of Sunni art is non-figural, there have been many examples of figural representations of Muhammad in illuminated manuscripts in the early modern period. These represent the Prophet in a couple of different ways, some more sensitive to general Sunni prohibitions than others. There are examples of the Prophet represented like any other person, with face fully shown. Others represent him as a figure with his face covered by a white veil, in acknowledgment of the prohibition against painting him.
In many of these miniatures, Muhammad is singled out of a crowd by a flame, much like a halo or nimbus, which is painted around his head or his entire body. It should be stressed, however, that these images represent the minority view about figural representation, and that they are not common in the Sunni world, which adheres more strictly to the an-iconic mode of representation. Finally, the prohibition against figural representation does not seem to have prevented the proliferation of images of Ali and other Shi‘i imams in popular Shi‘i culture.
What was common in Sunni art was the elaboration of a different type of icon of Muhammad, one that contained no pictures at all but symbolized and represented him nonetheless. This was a type of icon composed entirely of words, in Arabic calligraphy, written out in the shape of a sandal. The words could be a standard description of Muhammad's physical appearance, a literary genre called shama'il, or simple invocations for blessings. The sandal, called a hilya, became a regular shape for these types of an-iconic "pictures." The description of the Prophet is itself devotional. Culled from several reports narrated on the authority of his Companions, it is an example of austerity and moderation. One typical text reads:
When Ali described God's Messenger (peace and blessings be upon him), he said:
"God's Messenger (peace and blessings be upon him) was neither tall nor short, and he was of average height. His hair was neither tightly curled nor straight; it was loosely curled. He was neither plump nor chubby-cheeked, and in his face there was a rounded quality. He was white with a reddish tinge, dark black-eyed, with long eyelashes. He had splendid kneecaps, elbow joints and shoulder blades, free from hair. He had a strip of hair from the top of the chest to the navel. The palms of his hands and the soles of his feet were thick. When he walked, he moved as if he were walking on a slope, and when he looked around, he turned his whole torso, not just his neck. Between his shoulders was the Seal of Prophethood, for he is the Seal of the Prophets. He was the best of the people in generosity, the most truthful of the people in speech, the gentlest of them in temperament, and the noblest of them in social interactions. If someone saw him unexpectedly, he was awestruck by him, and if someone associated with him knowingly, he loved him. I have never seen the like of him (Peace and blessings be upon him), neither before nor after him." (from the "Book of Merits," by al-Tirmidhi, included in his Sunan)
This type of devotional description in calligraphy (a type of script which is highly developed in Islamic culture) is one method of circumventing the prohibition against figural icons. Another is simply calligraphy itself, which exists in a number of styles and is itself an art form in Islamic art, from manuscripts to copies of the Quran to inscriptions on everything from major monuments to household objects.