I’ve translated from the German the last portion of the Annals of Eutychius, who was Melkite Patriarch of Alexandria, and whose autograph manuscript has been edited in the CSCO.
33. EVENTS IN JERUSALEM AND LOWER EGYPT (820-830 A.D.)
. When morning came, the Patriarch Thomas and his companions were brought. The Muslims came and testified that the dome had enlarged (=been made larger). Patriarch Thomas disproved this through the (above-mentioned) argument 1.
 Abdallah ibn Daher said to them: he is right. Explain to me: How big was the dome, before it was removed, and how big is it now? They said: We will think about this. They went out and the meeting came to an end. Abdallah ibn Daher then went to Damascus. Thomas and his companions went merrily to the holy city.
 Thomas paid the Sheikh in question 1000 (dirhams). To him and his children after him as well as his children’s children the compensation was paid continuously, so long as (someone) from his descendants lived, until there was only one daughter (young woman). Elias ibn Mansur, Patriarch of the holy city, presented her with the compensation. Patriarch Thomas died, and his pupil named Basila (= Basilios) became Patriarch of the holy city. It was in the 7th year of the Caliphate of al-Ma`mun. Basila remained in the see 25 years and died. Abdallah ibn Daher returned to al-Ma`mun and reported about Egypt and on what he had undertaken (there). Then the (supporters of the) Emma (Yma) revolted. Al-’Emma is a coptic word and means “forty” 2. This is why: when the Romans left Egypt, in the time when the Muslims arrived, forty men stayed. In the lower part of the country (=Lower Egypt) they testified, multiplied and continued to do so and were called ‘Y MA, i.e. the descendants of the forty (men). They revolted and paid neither excise nor poll tax. This event was announced to Mamun and he sent his brother al-Mu`tasim, who was a Amir, to Egypt. The Emma fought against him . . . 3
1 The previous sentence in Ch. 51, 56,20-22 reads: A Muslim sheikh had secretly instructed him (to say): May the Emir ask them,”How big was the small dome, which I took down as you requested, and how big now is the dome, which I have rebuilt and enlarged?”
2 If the rebels had been descendants of those Romans left, then they would have used a Greek name, not a Coptic one. The letters given however do not permit the Coptic reading of HMA (for forty). Later historians have confounded this revolt with that of the Copts in Basmur, which took place allegedly under Abdel Malek around 750-51. Scholars are therefore divided on the exact date of the last Coptic revolt, therefore. See Sylvestre Chauleur, Histoire des Coptes d’Egyple, Paris 1960, 107 (dating the revolt to 216 AH. = 831 AD); item: C. Detlef, G. Müller. Grundzüge des christlich-islamischen Ägypten, Darmstadt 1969, 146 (both giving around 828-30).
3 The continuation of the sentence in Ch. (51, 57.17-18) reads: “and he fought them and killed very many of them. He struck them down and drove out their wives and children and brought them with him to Baghdad.”