Paul Richard in the Washington Post:
All depictions of Muhammad — or so we hear daily — are now and have always been forbidden in Islam. Art’s history disputes this. True, that strict taboo today is honored now by almost all Muslims, but old paintings of the prophet — finely brushed expensive ones, made carefully and piously by Muslims and for them — are well known to most curators of Islamic art.
There are numerous examples in public institutions in Istanbul, Vienna, Edinburgh, London, Dublin, Los Angeles and New York…
These portrayals of Muhammad are not big or new or common. Most were made for the elite. And most were bound in books. These were lavish volumes that were political in purpose, and were designed to celebrate and dignify self-promoting rulers. What their paintings show is this: Once upon a time — in the era of the caliphs and the sultans and the shahs, when the faithful felt triumphant, and courtly learning blossomed — the prophet did appear in great Islamic art.
Old portrayals of Muhammad come from Sunni lands and Shia ones, from the Turkey of the Ottomans, the India of the Mughals, from Uzbekistan, Afghanistan, Syria and Iran. The oldest that survive were painted circa 1300.
More here.