The Muslim scholar and muezzin Moosa al-Armani, who was a teacher in a madrasah (religious school) in Mosul, adopted a great approach to the conquest of Edessa, using psychological warfare to support
the campaign of Imad ad-Deen Zangi against Edessa in 539 AH/1145 CE. The scholar joined the siege as a fighter, and a smart idea occurred to him during Imad ad-Deen's siege of the city. He went to the marketplace and bought some Armenian-style clothing, then he entered the city wearing them, and the Crusaders did not recognize him or become suspicious about him.
He explains: "I went to the marketplace and bought some Armenian garments, and dressed as one of them. I went to the city to see what I could find out about it. I came to the mosque and went in, and I saw the minaret and said to myself: Let me ascent the minaret and give the adhan and see what happens. So I ascended and gave the call to prayer, 'Allahu akbar, Allahu akbar!' I gave the adhan. The infidels were on the walls, and the cry went up in the city that the Muslims had attacked the city from the other direction. So the infidels stopped fighting and came down from the walls, and the Muslims climbed up and attacked the city."
Excerpts from: Salah ad-Deen al-Ayubi - Volume one, by Dr. Ali M. Sallabi, International Islamic Publishing House