Was Al-Aqsa Mosque a trace or a building when the Prophet (peace be upon him) prayed in it?

The apparent meaning of the authentic hadiths indicates that the Mosque was already built on the night the Prophet, peace and blessings be upon him, was taken on his nocturnal journey (Isra'), whereas what is reported in history books is that the Mosque was built during the era of Umar ibn al-Khattab, may Allah be pleased with him.