Dragon gate (Arabic: باب الثعبان, Bāb al-Thu‘bān, 'Gate of the Serpent') is a door of Great Mosque of Kufa.
There is a Hadith in Bihar al-Anwar from Ja'far al-Sadiq says :
Amir al-Momenin was presenting a sermon on the rostrum in Kufa, when suddenly a dragon appeared, running severely towards the people and causing them to flee. Hadrat told the people "open the way for him" and the dragon came close and climbed up from the rostrum. He kissed the blessed feet of Hadrat and exhaled 3 times, before coming down and leaving. People asked for an explanation and Hadrat said "He was a man of the Jinn and was saying "One of the people(Ansar or patrons) named Jaber ibn-Sami' has killed his child by using stone but his child hadn't hurt Jaber in anyway". He was asking for revenge."
The name of the door, became "Dragon gate" or Dragon door. Also it has been said that Muawiyah I fastened an elephant there and the name of the door became "The elephant gate" for a while.