Theophanes'
Chronographia (written in the early 800s) under the year 635 says Umar tried to build the temple in Jerusalem but it fell to the ground. Then the Jews told him he needed to remove the cross from the Mount of Olives. After that was done he was able to build the building. The entry in Theophanes ends "for this reason the Christ-haters [
misochristoi] cast down many crosses." (From the 1839 edition of Theophanes by Johann Classen, with Latin translation.)
This could be the earlier allusion to the ACLU.
This may be a reference to the Mosque of Omar, which is said to have been built in 637. The Bazak Guide to Israel 1987-88, page 145, has an entry about the Dome of the Rock and says "erroneously also known as 'the Mosque of Omar' (which once stood nearby and was reduced to nothing).
Also according to Bazak, the Dome of the Rock was built in 691, so it is not the building mentioned by Theophanes.