Gibb H.A.R. The Armies of Saladin.
Gibb H.A.R. Studies on the Civilization of Islam. 1962
Mosul and the Jazira.
Ibn al-Athir, in his narrative of the Mosul expedition against Saladin in 571:1176, makes a valuable statement about the size of its forces. The askar of Mosul was accompanied in this campaign by the troops of all the vassal principalities, including Hisn Kaifa and Mardin. In a pointed refutation of Imadeddin's statement that their forces were reported to number 20,000, he says that they numbered "precisely" a little less than 6,500, and adds:
"I myself inspected the register of the review and the battle distribution of the askar between right and left wings, center, and advance guard, and the officer responsible for keeping the register was my brother Majdeddin. ... What, I should like to know, does al-Mawsil and its dependencies up to the Euphrates amount to, that it should be able to maintain for itself and in them 20,000 horsemen?"
The Chronicle of Ibn al-Athir for the Crusading Period from al-Kamil i’l-Ta’rikh. Part 2: The Years 541-589/1146-1193: The Age of Nur al-Din and Saladin. Translated by D.S. Richards. 2007
This came about because, after the defeat of his brother, ‘Izz al-Dîn Mas'üd, by Saladin in the previous year and after his coming to terms with his [other] brother, ‘Imad al-Dîn the lord of Sinjâr, Sayf al-Dîn returned to Mosul, gathered his troops, distributed money to them and asked for support from the lord of Hisn Kayfâ, the lord of Mardin and others. Large forces assembled with him, whose number reached 6,000 horse.
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The two armies came into contact at Sultan’s Hill. Sayf al-Dîn had arrived first and when Saladin arrived, it was already the evening and he and his men were tired and thirsty. They threw themselves down on the ground, unable to move further. Several persons advised Sayf al-Dîn to attack them while they were in this state, but Zulfandâr said, ‘We have no need to engage this rebel at this hour. Tomorrow early we shall seize them all.’ Sayf al-Dîn therefore put off the battle until the next day.
In the morning they drew up their battle lines. Zulfandâr, who was the commander of Sayf al-Dîn’s army, placed his banners in a depression in the land where they could only be seen by those who were close to them. When the men could not see them, they imagined that the sultan had fled the field, so they did not stand firm but fled, everyone looking out for himself. From both sides, despite their large numbers, only one person was killed.
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The Secretary ‘Imâd al-Dîn mentioned in his book al-Barq al-Shcımî' on the history of Saladin’s reign that Sayf al-Dîn’s army at this battle numbered 20,000 cavalry. That was not so. It was quite certainly more than 6,000 horse but less than 6,500, for I have perused the review register. The official who administered and wrote it was my brother Majd al-Dîn Abü’l-Sa‘âdât al-Mubârak ibn Muhammad ibn ‘Abd al-Karîm (God have mercy in him). Al-Tmâd’s intention was simply to exaggerate the deeds of his master by stating that with 6,000 he defeated 20,000, but the truth better deserves to be followed. What is more, I wish I knew how large is Mosul with its dependencies up to the Euphrates that it could have and maintain 20,000 cavalry!