Source, in full
This was supposedly said by Charles when Martin Luther appeared at the Diet of Worms (16–18 April 1521) under an imperial safe-conduct; members of the pro-papal party (sometimes Johann Maier von Eck (Eccius) is specified) are supposed to have urged the emperor to seize Luther in despite of the safe-conduct, whereupon Charles alluded to the story that when Jan Huss had appeared at the Council of Constance before the Emperor Sigismund under a similar safe-conduct and had been arrested anyway, Huss reproached Sigismund, who visibly reddened at his own lack of faith. The quotation appears in various similar forms, e.g., "I shall not blush as Sigismund did at Constance." The saying is attributed to Charles by the German scholars, poets, and brothers Wilhelm and Gabriel Seyfried in their Dissertatio Historica de Johanne Hus (Jena, 1711), p. 99, without a specific source, in the Latin form Nolo cum Sigismondo, Antecessore meo erubescere.