Summoned before the emperor Charles V and the assembled estates of the empire in April 1521, under an imperial safe conduct that many advised him not to trust given what had happened to Hus at Constance, Luther was shown his books and asked whether they were his and whether he would recant. He asked for a day to consider, and returned with an answer distinguishing among his writings and refusing to retract what could not be shown contrary to scripture and plain reason, since he could not act against conscience.
The most quoted sentence of the Reformation, here I stand, I can do no other, does not appear in the earliest reports. It seems to have entered the record in the printed accounts shortly afterwards. The refusal itself is thoroughly attested and the substance of the answer is not in doubt; the ringing line is a later addition, and the atlas marks it as such rather than repeating it as a quotation.
The Edict of Worms followed in May, declaring Luther an outlaw whose books were to be burned, whose adherents were liable to forfeiture, and who might be killed without legal penalty. It was never effectively enforced across the empire, because enforcement depended on territorial rulers and many of them declined.