 When the Peasant War broke out, Karlstadt was threatened and wrote to Luther and asked for assistance.Luther took him in, and Karlstadt lived secretly in Luther's house for eight weeks.However, Karlstadt had to sign a pseudo retraction, titled “Apology by Dr. Andreas Karlstadt Regarding the False Charge of Insurrection Which has Unjustly Been Made Against Him.” 
It also contained a preface by Luther.