Article 1, Section 9, Clause 2: William Blackstone, Commentaries 3:129--37

"In a former part of these commentaries we expatiated at large on the personal liberty of the subject. It was shewn to be a natural inherent right, which could not be surrendered or forfeited unless by the commission of some great and atrocious crime, nor ought to be abridged in any case without the special permission of law. A doctrine co-eval with the first rudiments of the English constitution; and handed down to us from our Saxon ancestors, notwithstanding all their struggles with the Danes, and the violence of the Norman conquest: asserted afterwards and confirmed by the conqueror himself and his descendants: and though sometimes a little impaired by the ferocity of the times, and the occasional despotism of jealous or usurping princes, yet established on the firmest basis by the provisions of magna carta, and a long succession of statutes enacted under Edward III. To assert an absolute exemption from imprisonment in all cases, is inconsistent with every idea of law and political society; and in the end would destroy all civil liberty, by rendering it's protection impossible: but the glory of the English law consists in clearly defining the times, the causes, and the extent, when, wherefore, and to what degree, the imprisonment of the subject may be lawful. This induces an absolute necessity of expressing upon every commitment the reason for which it is made; that the court upon an habeas corpus may examine into it's validity; and according to the circumstances of the case may discharge, admit to bail, or remand the prisoner."