Mormon History, Dec 4, 1845, Thursday

[William Clayton Writings] Thursday 4th. ... Went up into the Temple. The brethren are very busy preparing the room for work. ... Evening met with the first quorum in the Attic story of the Temple for prayer.

[source: Fillerup, Robert C., compiler; William Clayton Nauvoo Diaries and Personal Writings, A chronological compilation of the personal writings of William Clayton while he was a resident of Nauvoo, Illinois. http://www.boap.org/LDS/Early-Saints/clayton-diaries]