Muhammad ibn Ya‘qub, from Ahmad ibn Idris, from Muhammad ibn Abdul-Jabbar, who said: I wrote to Abu Muhammad عليه السلام, peace be upon him, asking Him عليه السلام: "Is it permissible to pray in a cap made of pure silk or a cap made of brocade (dibaj)?" Imam عليه السلام wrote in reply: "Prayer is not permissible in pure silk."