Ayodhya was the capital city of King Dasrath. It was the place from where sage Vishwamitra had taken Shri Ram and Lakshman to save his “yagna”.
Valmiki Ramayan 1/5, 6, all chapters and other references, Shri Ram Charitmanas 1/15/1: 1/34/2, 3: 1/189/1 to 1/207/4: 2/0/1 to 2/187/1 there are many references.